Crystal growth method, crystal growth apparatus, group-III nitride crystal and group-III nitride semiconductor device

ABSTRACT

A crystal growth method, comprising the steps of: a) bringing a nitrogen material into a reaction vessel in which a mixed molten liquid comprising an alkaline metal and a group-III metal; and b) growing a crystal of a group-III nitride using the mixed molten liquid and the nitrogen material brought in by the step a) in the reaction vessel, wherein a provision is made such as to prevent a vapor of the alkaline metal from dispersing out of the reaction vessel.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a crystal growth method, acrystal growth apparatus, a group-III nitride crystal, and a group-IIInitride semiconductor device. In particular, the present inventionrelates to a crystal growth method and a crystal growth apparatus for agroup-III nitride crystal, the group-III nitride crystal, and agroup-III nitride semiconductor device-employing the group-III nitridecrystal applicable to a blue light source for an optical disk drive, forexample.

[0003] 2. Description of the Related Art

[0004] Now, a InGaAlN-family (group-III nitride) device used as violetthrough blue through green light sources is produced by a crystal growthprocess employing an MO-CVD method (organic metal chemical vapor phasegrowth method), an MBE method (molecular beam crystal growth method),etc. on a sapphire or SiC substrate in most cases. In using sapphire orSiC as a substrate, crystal defect caused due to a large expansivitydifference and/or lattice constant difference from a group-III nitridemay occur frequently. By this reason, there is a problem that the devicecharacteristic may become worth, it may be difficult to lengthen thelife of the light-emission device, or the electric power consumption maybecome larger.

[0005] Furthermore, since a sapphire substrate has an insulatingproperty, drawing of an electrode from the substrate like in anotherconventional light-emission device is impossible, and therefore, drawingthe electrode from the nitride semiconductor surface on which crystalwas grown is needed. Consequently, the device area may have to beenlarged, and, thereby, the costs may increase. Moreover, chipseparation by cleavage is difficult for a group-III nitridesemiconductor device produced on a sapphire substrate, and it is noteasy to obtain a resonator end surface needed for a laser diode (LD) bycleavage, either. By this reason, a resonator end surface formationaccording to dry etching, or, after grinding a sapphire substrate to thethickness of 100 micrometers or less, a resonator end surface formationin a way near cleavage should be performed. Also in such a case, it isimpossible to perform formation of a resonator end surface and chipseparation easily by a single process like for another conventional LD,and, also, complication in process, and, thereby, cost increase mayoccur.

[0006] In order to solve these problems, it has been proposed to reducethe crystal defects by employing a selective lateral growth methodand/or another technique for forming a group-III nitride semiconductorfilm on a sapphire substrate.

[0007] For example, a document ‘Japanese Journal of Applied Physics,Vol. 36 (1967), Part 2, No. 12A, pages L1568-1571’ (referred to as afirst prior art, hereinafter) discloses a laser diode (LD) shown inFIG. 1. This configuration is produced as follows: After growing up aGaN low-temperature buffer layer 2 and a GaN layer 3, one by one, on asapphire substrate 1 by an MO-VPE (organometallic vapor phase epitaxy)apparatus, an SiO₂ mask 4 for selective growth is formed. This SiO₂ mask4 is formed through photo lithography and etching process, afterdepositing a SiO₂ film by another CVD (chemistry vapor phase deposition)apparatus. Next, on this SiO₂ mask 4, again, a GaN film 3′ is grown upto a thickness of 20 micrometers by the MO-VPE apparatus, and, thereby,GaN grows laterally selectively, and, as a result, the crystal defectsare reduced as compared with the case where the selective lateral growthis not performed. Furthermore, prolonging of the crystal defect towardan activity layer 6 is prevented by provision of a modulation dopedstrained-layer superlattice layer (MD-SLS) 5 formed thereon.Consequently, as compared with the case where the selective lateralgrowth and modulation doped strained-layer superlattice layer are notused, it becomes possible to lengthen the device life.

[0008] In the case of this first prior art, although it becomes possibleto reduce the crystal defects as compared with the case where theselective lateral growth of a GaN film is not carried out on a sapphiresubstrate, the above-mentioned problems concerning the insulatingproperty and cleavage by using a sapphire substrate still remain.Furthermore, as the SiO₂ mask formation process is added, the crystalgrowth by the MO-VPE apparatus is needed twice, and, thereby, a problemthat a process is complicated newly arises.

[0009] As another method, for example, a document ‘Applied PhysicsLetters, Vol. 73, No. 6, pages 832-834 (1998)’ (referred to as a secondprior art, hereinafter) discloses application of a GaN thick filmsubstrate. By this second prior art, a GaN substrate is produced, bygrowing up a 200-micrometer GaN thick film by an H-VPE (hydride vaporphase growth) apparatus after 20-micrometer selective lateral growthaccording to the above-mentioned first prior art, and, then, grindingthe GaN substrate thus having grown to be the thick film from the sideof the sapphire substrate so that it may have the thickness of 150micrometers. Then, the MO-VPE apparatus is used on this GaN substrate,crystal growth processes required for a LD device are performed, one byone, and, thus, the LD device is produced. Consequently, it becomespossible to solve the above-mentioned problems concerning the insulatingproperty and cleavage by using the sapphire substrate in addition tosolving the problem concerning the crystal defects.

[0010] A similar method is disclosed by Japanese Laid-Open PatentApplication No. 11-4048. FIG. 7 shows a typical figure thereof.

[0011] However, further, the process is more complicated in the secondprior art, and, requires the higher costs, in comparison to the firstprior art. Moreover, in growing up the no less than 200 micrometer GaNthick film by the method of the second prior art, a stress occurring dueto a lattice constant difference and a expansivity difference from thesapphire of the substrate becomes large, and a problem that thecurvature and the crack of the substrate arise may newly occur.Moreover, even by performing such a complicated process, the crystaldefective density can be reduced to only on the order of 10⁶/cm². Thus,it is not possible to obtain a practical semiconductor device.

[0012] In order to avoid this problem, setting to 1 mm or more thicknessof an original substrate (sapphire and spinel are the most desirablematerials as the substrate) from which a thick film grows is proposed byJapanese Laid-Open Patent Application No. 10-256662. According thereto,no curvature nor crack arise in the substrate even when the GaN filmgrows in 200 micrometers of thickness by applying this substrate havingthe thickness of 1 mm or more. However, a substrate thick in this wayhas a high cost of the substrate itself, and it is necessary to spendmuch time on polish thereof, and leads to the cost rise of the polishprocess. That is, as compared with the case where a thin substrate isused, the cost becomes higher by using the thick substrate. Moreover,although no curvature nor crack arise in the substrate after growing upthe thick GaN film in using the thick substrate, curvature and/or crackmay occur as stress relief occurs during the process of polish. By thisreason, even when the thick substrate is used, the GaN substrate havinga high crystal quality and having such a large area that it can bepractically used for an ordinary semiconductor device manufacturingprocess cannot be easily produced.

[0013] A document ‘Journal of Crystal Growth, Vol. 189/190, pages.153-158 (1998)’ (referred to as a third prior art, hereinafter)discloses that a bulk crystal of GaN is grown up, and it is used as ahomoepitaxial substrate. According to this technique, under the hightemperature in the range between 1400 and 1700° C., and under the veryhigh nitrogen pressure of 10 kilobars, crystal growth of the GaN isperformed from a Ga liquid. In this case, it becomes possible to grow upa group-III nitride semiconductor film required for a device by usingthis GaN substrate. Therefore, it is possible to provide the GaNsubstrate without needing the process complicate like in theabove-described first and second prior arts.

[0014] However, by this third prior art, crystal growth in hightemperature and high pressure is needed, and, thus, there is a problemthat a reaction vessel which can resist these conditions should be veryexpensive. In addition, even when such a growth method is employed, thesize of the crystal obtained has the problem of being too small, i.e.,at most on the order of 1 cm, and, thus, it is too small to put it inpractical use of semiconductor device manufacture.

[0015] The GaN crystal growth method using Na which is an alkaline metalas a flux is proposed by a document ‘Chemistry of Materials, Vol. 9(1977), pages 413-416’ (referred to as a fourth prior art, hereinafter)as a technique of solving the problem of GaN crystal growth in theabove-mentioned high temperature and high pressure. According to thistechnique, sealing sodium azide (NaN₃) and Ga metal used as a flux and amaterial into a reaction vessel made from stainless steel (vessel innerdimension: diameter=7.5 mm and length=100 mm) in nitrogen atmosphere,and the reaction vessel is maintained in the temperature in the rangebetween 600 and 800° C. for 24 to 100 hours to grow up a GaN crystal. Inthe case of this fourth prior art, crystal growth at the comparativelylow temperature in the range between 600 and 800° C. can be achieved,and, also, the require pressure inside the vessel should be only on theorder of 100 kg/cm², which is comparatively lower than the case of thethird prior art. However, in this fourth prior art, the size of thecrystal obtained is small as less than 1 mm which is too small to be putinto practical use in semiconductor device manufacture, like in the caseof the third prior art.

[0016] Therefore, the applicant of the present application has proposeda method of enlarging a group-III nitride crystal. However, in themethod, nucleus generation initiates of the crystal growth is naturalnucleus generation, and, thus, a large number of nucleus are undesirablygenerated. In order to control this nucleus generation, the applicanthas proposed to utilize a seed crystal in the U.S. patent applicationSer. No. 09/590,063, filed on Jun. 8, 2000, by Seiji Sarayama et al.(the entire contents of which are hereby incorporated by reference).However, there is a problem that a required crystal growth apparatusbecomes complicated. Therefore, it has been demanded to realize a methodfor effectively controlling nucleus generation, while achieving a simpleapparatus configuration of a conventional flux method, in order to solvethis problem.

[0017] Further, Japanese Laid-Open Patent Application No. 2000-327495discloses a fifth prior art combining the above-mentioned fourth priorart and an epitaxial method utilizing a substrate. In this method, asubstrate on which GaN or AlN is grown previously is used, and, thereon,a GaN film according to the fourth prior art is grown. However, in thismethod, as it is basically the epitaxial method, the problem of crystaldefects occurring in the above-mentioned first and second prior artcannot be solved. Further, as the GaN film or AlN film should be grownon the substrate previously, the process becomes complicated, and,thereby, the costs increase.

[0018] Furthermore, recently, Japanese Laid-Open Patent ApplicationsNos. 2000-12900 and 2000-22212 disclose a sixth prior art in which aGaAs substrate is used and a GaN thick-film substrate is produced. Inthis method, a GaN film having a thickens in a range between 70 μm and 1mm is selectively grown on a GaAs substrate by using an SiO₂ film or SiNfilm as a mask as in the above-mentioned first prior art, as shown inFIGS. 3A through 3C. The crystal growth there is performed by the H-VPEapparatus. Then, the GaAs substrate is etched and thus removed by usingaqua regia. Thus, the GaN self-standing substrate is produced, as shownin FIG. 3D. By using this GaN-self standing substrate, a GaN crystalhaving a thickness of several tens of millimeters is grown by vaporphase epitaxy by the H-VPE apparatus again, as shown in FIG. 4A. Then,this GaN crystal of several tens millimeters is cut into wafer shapes bya slicer, as shown in FIG. 4B. Thus, GaN wafers are produced, as shownin FIG. 4C.

[0019] According to this sixth prior art, the GaN self-standingsubstrate can be obtained, and, also, the GaN crystal having thethickness of several tens of millimeters can be obtained. However, thismethod has the following problems:

[0020] {circle over (1)} As the SiN film or SiO² film is used as a maskfor selective growth, the manufacturing process becomes complicated,and, thus, the costs increase;

[0021] {circle over (2)} When the GaN crystal having the thickness ofseveral tens millimeters is grown by the H-VPE apparatus, GaN crystals(in monocrystal or polycrystal) or amorphous GaN having a similarthickness adhere to the inner wall of the reaction vessel. Accordingly,the productivity is degraded thereby.

[0022] {circle over (3)} As the GaAs substrate is etched and removedevery time of the crystal growth as a sacrifice substrate, the costsincrease thereby.

[0023] {circle over (4)} With regard to the crystal quality, problems oflattice mismatch due to crystal growth on a different-substancesubstrate, and a high defect density due to difference in expansivityremain.

SUMMARY OF THE INVENTION

[0024] An object of the present invention is to achieve a group IIInitride crystal having a sufficient size such that a semiconductordevice, such as a high-efficient light emitting diode or LD can beproduced therefrom, without complicating the process which is theproblem in the above-mentioned first or the second prior art, withoutusing an expensive reaction vessel which is the problem in the thirdprior art, and without provision of insufficient size of the crystalwhich is the problem in the third and fourth prior arts, and, also,solving the above-mentioned problems in the fifth and sixth prior arts,and a crystal growth method and a crystal growth apparatus by which sucha group-III nitride crystal can be manufactured, and a high-performancegroup-III nitride semiconductor device.

[0025] A crystal growth method according to the present invention,includes the steps of:

[0026] a) providing a nitrogen material into a reaction vessel in whicha mixed molten liquid comprising an alkaline metal and a group-IIImetal; and

[0027] b) growing a crystal of a group-III nitride using the mixedmolten liquid and the nitrogen material provided in the step a) in thereaction vessel,

[0028] wherein a provision is made such as to prevent a vapor of thealkaline metal from dispersing out of the reaction vessel.

[0029] Thereby, when growing up the group-III nitride crystal in thereaction vessel especially using the alkaline metal and the mixed moltenliquid which contains group-III metal at least and the nitrogen materialbrought from the outside of the reaction vessel, the alkaline metalvapor is prevented from dispersing out of the reaction vessel. Thereby,evaporation of the alkaline metal out of the reaction vessel andcondensation thereof can be prevented and it becomes possible to avoidobstruction against supply of the nitrogen material, and thus change ofmaterial composition. Consequently, the crystal growth can be wellcontrolled, and a satisfactory group-III nitride crystal can be grown upstably.

[0030] A crystal growth method according to another aspect of thepresent invention includes the steps of:

[0031] a) providing a nitrogen material into a reaction vessel in whicha mixed molten liquid comprising an alkaline metal and a group-IIImetal; and

[0032] b) growing a crystal of a group-III nitride using the mixedmolten liquid and the nitrogen material provided in the step a) in thereaction vessel,

[0033] wherein a provision is made such as to prevent a vapor of thealkaline metal from blocking a zone through which the nitrogen materialis supplied from the outside of the reaction vessel.

[0034] Thereby, the nitrogen material brought in from the outside of thereaction vessel can be prevented from being blocked by the condensedalkaline metal.

[0035] Consequently, the crystal growth can be well controlled, and, asatisfactory group-III nitride crystal can be grown up stably.

[0036] For this purpose, the temperature in the reaction vessel abovethe surface of the mixed molten liquid may be preferably controlled soas to prevent the vapor of the alkaline metal from condensing.

[0037] The temperature of the above-mentioned zone may preferably becontrolled for the same purpose.

[0038] Further, another reaction vessel may be provided outside of thereaction vessel;

[0039] the nitrogen material may be brought into the reaction vesselthrough this outer reaction vessel; and

[0040] a provision may preferably be made such as to allow the nitrogenmaterial to be brought into the originally provided inner reactionvessel from the outer reaction vessel, and, also, to prevent the vaporof the alkaline metal from dispersing out of the inner reaction vessel,for the above-mentioned object.

[0041] The nitrogen material may be preferably supplied horizontally orfrom a direction below the horizontal direction.

[0042] Thereby, condensation of the alkaline metal vapor in the zonethrough which the nitrogen material is supplied can be prevented.

[0043] A crystal growth apparatus according to the present inventionincludes:

[0044] a reaction vessel holding a mixed molten liquid comprising analkaline metal and a group-III metal;

[0045] a first heating device heating the mixed molten liquid so as toenable crystal growth therein; and

[0046] a second heating device heating above the surface of the mixedmolten liquid so as to prevent the vapor of the alkaline metal above thesurface of the mixed molten liquid from condensing.

[0047] A crystal growth apparatus according to another aspect of thepresent invention includes:

[0048] a reaction vessel holding a mixed molten liquid comprising analkaline metal and a group-III metal; and

[0049] a heating device heating a zone through which a nitrogen materialis supplied externally into the reaction vessel.

[0050] Thereby, a complicated process described above for the first orsecond prior art is not needed, but it becomes possible to obtain ahigh-quality group-III nitride crystal at low cost. Furthermore, therequired growth temperature is as low as less than 100° C., and, also,the required growth pressure is as low as less than 100 kg/cm², for thecrystal growth of the group-III nitride. Accordingly, it is notnecessary to use an expensive reaction vessel which can resist asuper-high pressure and a super-high temperature as in theabove-mentioned third prior art. Consequently, it becomes possible atlow cost to obtain a group-III nitride crystal. Moreover, since it islow temperature and low pressure needed for the crystal growth, itbecomes possible by using a seed crystal as a nucleus to enlarge thesize of the group-III nitride crystal by carrying out crystal growth.

[0051] A crystal growth method according to another aspect of thepresent invention includes the steps of:

[0052] a) carrying out crystal growth in a reaction vessel of agroup-III nitride comprising a group-III metal and a nitrogen from analkaline metal, a substance comprising the group-III metal, and asubstance comprising the nitrogen; and

[0053] b) maintaining a growth condition for a crystal the group-IIInitride at a condition at which the crystal growth starts; then,

[0054] c) maintaining the growth condition at a condition at which thecrystal growth stops; and, then,

[0055] d) again setting the condition at which the crystal growthstarts.

[0056] Thus, by setting the crystal growth condition enabling thecrystal growth and then setting the other crystal growth condition notenabling the crystal growth, a crystal nucleus can be grown selectively.That is, by setting again the crystal growth condition enabling thecrystal growth, the crystal growth progresses further from this crystalnucleus. By repeating such a control of the crystal growth condition asthat the crystal growable condition is entered and exited from, it ispossible to control generation of crystal nucleus, in comparison to acase where no such a control is performed. Thus, it becomes possible togrow the group-III nitride crystal to have a large size effectively, andthus to effectively utilize the materials therefor. As a result, it ispossible to obtain a large-sized group-III nitride crystal at low cost.

[0057] Further, in comparison to a seed-crystal method in the relatedart in which a position of a crystal nucleus supplied externally as aseed crystal is controlled, the apparatus is not needed to be socomplicated, and, thus, the total cost can be reduced, according to thepresent invention.

[0058] Specifically, the step b) may maintain the temperature of a zonein which a crystal of the group-III nitride grows at a temperature atwhich the crystal growth starts;

[0059] the step c) may lower the temperature of the zone to atemperature such that no alloy is formed between the group-III metal andanother metal, and maintaining this temperature; and

[0060] the step d) may increase the temperature to the temperature atwhich the crystal growth starts again.

[0061] The increase and decrease of the temperature may be preferablyperformed several times.

[0062] The substance comprising the nitrogen may be of a gas, and thegas may be supplied into the reaction vessel continuously at apredetermined pressure. Thereby, it is possible to control the crystalgrowth reaction only by control of the temperature. As a result, it ispossible to control a change in growth parameter in the crystal growth,and, also, by continuously supplying the nitrogen material, ahigh-quality group-III nitride crystal can be grown with little nitrogenloss.

[0063] The substance comprising the group-III metal may preferably beadditionally provided at a time of the temperature is lowered.

[0064] Thereby, it is possible to avoid a situation of unexpectedinterruption of the crystal growth occurring due to exhaustion of thegroup-III material. Furthermore, it is possible to effectively preventchange of the ratio in amount among the group-III material and group-Vmaterial, and the alkaline metal used as the flux. As a result, it ispossible to achieve stable crystal growth wherein the crystal quality isfixed stably, and, thus, it is possible to grow up a high-qualitygroup-III nitride crystal.

[0065] Furthermore, as the timing of the additional supply of thegroup-III material is in an interval in which the crystal growth isterminated, it is possible to effectively control change in growparameter such as temperature change, material amount ratio change andso forth which may otherwise adversely affect the proper crystal growth.Also by this point, the crystal growth for a high-quality group-IIInitride crystal can be more positively achieved.

[0066] The above-mentioned step b) may instead maintain an effectivepressure of the substance comprising the nitride in a form a gas in azone in which a crystal of the group-III nitride grows at a pressure atwhich the crystal growth starts;

[0067] the step c) may lower the effective pressure of the nitrogen gasin the zone to a pressure such that the crystal growth stops, andmaintaining this pressure; and

[0068] the step d) may increase the effective pressure of the nitrogengas to the pressure at which the crystal growth starts again.

[0069] Further, a crystal growth apparatus which carries out crystalgrowth of the group-III nitride crystal which has the features describedabove can be realized at low cost in addition to the above-mentionedeffects.

[0070] Furthermore, by carrying out the crystal growth according to anyone of the above-described methods and/or the above-mentionedapparatuses, it becomes possible to realize a large-sized group-IIInitride crystal by which a semiconductor device may be produced in apractical manner at low cost.

[0071] Furthermore, by producing the group-III nitride semiconductordevice using the group-III nitride crystal mentioned above, a highlyefficient device is realizable at low cost. This group-III nitridecrystal is a high-quality crystal having few crystal defects, asmentioned above. Thus, a highly efficient device is realizable by deviceproduction from thin film growth using this group-III nitride crystal,or using it as a substrate of the device. That is, a high output whichhas not been realized conventionally can be provided by the device and along life of the device is achieved in a case of production of asemiconductor laser or a light emitting diode therefrom. In a case ofproduction of an electronic device therefrom, low power consumption, lownoise, high-speed operation, and high temperature operation areachievable therefrom. In a case of light receiving device, low noise anda long life can be obtained therefrom.

[0072] A crystal growth method according to another aspect of thepresent invention includes the steps of:

[0073] a) forming a mixed molten liquid comprising an alkaline metal anda substance comprising a group-III metal in a liquid holding vessel;

[0074] b) growing in the liquid holding vessel a crystal of a group-IIInitride comprising the group-III metal and nitride from the mixed moltenliquid and a substance comprising the nitride;

[0075] c) creating a local concentration distribution of dissolvednitrogen in the mixed molten liquid in the liquid holding vessel duringthe step b).

[0076] Thereby, without making the process complicated as in the firstand second prior arts described above, since the local concentrationdistribution of the dissolved nitrogen is produced in the mixed moltenliquid, it becomes possible to avoid use of an expensive reaction vesselas in the third prior art, and the size of the produced crystal can beenlarged in contrast to the third and fourth prior art. Thus, thegroup-III nitride crystal of a practical size for producingsemiconductor devices, such as a highly efficient light emitting diodeand LD, can be grown up.

[0077] Furthermore, the necessary growth temperature is as low as 1000degrees C. or less, and, also, the necessary growth pressure is as lowas approximately 100 or less atm. Thereby, it is not necessary to use anexpensive reaction vessel which can resist a super-high pressure and asuper-high temperature as in the third prior art. Consequently, itbecomes possible to realize the device using the group-III nitridecrystal at low cost.

[0078] Furthermore, by producing the local concentration (uneven)distribution of the dissolved nitrogen in the mixed molten liquid, itbecomes possible to limit a location of occurrence of nucleus generationof the group-III nitride crystal to a specific part of the mixed moltenliquid, and the group-III nitride crystal having a large size can thusbe grown up.

[0079] The liquid holding vessel may have an inner shape such as toproduce the local concentration distribution of the dissolved nitrogenin the mixed molten liquid.

[0080] The inner shape of the liquid holding vessel may be such that thecross sectional area becomes smaller downward.

[0081] The inner shape of the liquid holding vessel may instead be suchthat the cross sectional area is reduced partially (at a specificheight).

[0082] The inner shape of the liquid holding vessel may future insteadbe such that the cross sectional area becomes smaller downward first,and, then, the cross sectional area is uniform downward from the midlevel (height).

[0083] The inner shape of the liquid holding vessel may further insteadbe such that the cross sectional area becomes smaller downward first,and, then, the cross sectional area becomes larger downward from the midlevel.

[0084] A crystal growth apparatus according to another aspect of thepresent invention includes:

[0085] a liquid holding vessel in which a mixed molten liquid comprisingan alkaline metal and a substance comprising a group-III metal isformed; and

[0086] a unit growing in the liquid holding vessel a crystal of agroup-III nitride comprising the group-III metal and nitride from themixed molten liquid and a substance comprising the nitride, and,

[0087] wherein the liquid holding vessel has an inner shape such as toproduce a local concentration distribution of dissolved nitrogen in themixed molten liquid (as mentioned above in the crystal growth methods).

[0088] The above-mentioned unit may include a heating device heating thetemperature inside the liquid holding vessel so as to enable the crystalgrowth therein.

[0089] The unit may include a plurality of heating devices for creatinga predetermined temperature difference between an upper part and a lowerpart of the liquid holding vessel independently.

[0090] Thus, since the cross sectional area of the vessel becomessmaller downward, and, then, it is uniform from the mid level, or itbecomes larger from the mid level, the mixed molten liquid may be heldto this zone. Consequently, the group-III metal can be continuouslysupplied therefrom to a specific zone in which the crystal nucleus isgenerated, and, thereby, it becomes possible to grow up a large-sizedgroup-III nitride crystal.

[0091] Moreover, the group-III nitride crystal thus produced has a highquality (few crystal defects), and also, has a large size such as to bepractically utilized for producing a semiconductor device, and such agroup-III nitride crystal can be produced at low cost.

[0092] Moreover, since it is the semiconductor device produced using thegroup-III nitride crystal according to the present invention describedabove, a highly efficient group-III nitride semiconductor device can beoffered at low cost.

[0093] Furthermore, by producing the group-III nitride semiconductordevice using the group-III nitride crystal mentioned above, a highlyefficient device is realizable at low cost. As this group-III nitridecrystal is a high-quality crystal having few crystal defects, asmentioned above, a highly efficient device is realizable by deviceproduction from thin film growth using this group-III nitride crystal,or using it as a substrate of the device. That is, a high output whichhas not been realized conventionally can be provided and a long life isprovided in a case of production of a semiconductor laser or a lightemitting diode. In a case of production of an electronic device, lowpower consumption, low noise, high-speed operation, and high temperatureoperation are achievable. In a case of light receiving device, low noiseand a long life can be obtained.

[0094] Moreover, according to the present invention, the semiconductordevice may be a light-emission device which emits light of thewavelength shorter than 400 nm, and can emit light at high efficiencyalso in this wavelength region. That is, since the semiconductor devicethus obtained has few crystal defects and few impurities consequently,it becomes possible to realize the efficient light-emissioncharacteristic wherein light emission from a deep level is wellcontrolled.

BRIEF DESCRIPTION OF THE DRAWINGS

[0095] Other objects and further features of the present invention willbecome more apparent from the following detailed description when readin conjunction with the following accompanying drawings.

[0096]FIG. 1 shows a side-elevational sectional view of a semiconductorlaser in the first prior art;

[0097]FIG. 2 shows a side-elevational sectional view of a semiconductorlaser in the second prior art;

[0098]FIGS. 3A through 3D and 4A through 4C illustrate the sixth priorart;

[0099]FIG. 5 shows a side-elevational sectional view of a crystal growthapparatus in a first embodiment of the present invention;

[0100]FIG. 6 shows a side-elevational sectional view of a crystal growthapparatus in a second embodiment of the present invention;

[0101]FIG. 7 shows a side-elevational sectional view of a crystal growthapparatus in a third embodiment of the present invention;

[0102]FIG. 7 shows a side-elevational sectional view of a crystal growthapparatus in a fourth embodiment of the present invention;

[0103]FIG. 9 shows a perspective view of one example of a semiconductorlaser to which a group-III nitride semiconductor device according to thepresent invention is applied;

[0104]FIG. 10 shows a side-elevational sectional view of a crystalgrowth apparatus in a fifth embodiment of the present invention;

[0105]FIG. 11 illustrates a temperature control sequence in the fifthembodiment of the present invention;

[0106]FIG. 12 shows a side-elevational sectional view of a crystalgrowth apparatus in a first variant embodiment of the fifth embodimentof the present invention;

[0107]FIG. 13 illustrates a temperature control sequence in the firstvariant embodiment of the fifth embodiment of the present invention;

[0108]FIG. 14 illustrates a pressure control sequence in a secondvariant embodiment of the fifth embodiment of the present invention;

[0109]FIG. 15 illustrates a pressure control sequence in a third variantembodiment of the fifth embodiment of the present invention;

[0110]FIG. 16 shows a side-elevational sectional view of a crystalgrowth apparatus in a sixth embodiment of the present invention;

[0111]FIG. 17 shows an elevational sectional view of a first example ofa mixed molten liquid vessel in the crystal growth apparatus in thesixth embodiment of the present invention;

[0112]FIG. 18 shows an elevational sectional view of a second example ofthe mixed molten liquid vessel in the crystal growth apparatus in thesixth embodiment of the present invention;

[0113]FIG. 19 shows a side-elevational sectional view of a crystalgrowth apparatus in a seventh embodiment of the present invention;

[0114]FIG. 20A shows an elevational sectional view of a first example ofa mixed molten liquid vessel in the crystal growth apparatus in theseventh embodiment of the present invention; and

[0115]FIG. 20B shows an elevational sectional view of a second exampleof the mixed molten liquid vessel in the crystal growth apparatus in theseventh embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0116] Hereafter, embodiments of the present invention will now bedescribed with reference to the figures.

[0117] The present invention is characterized by preventingalkaline-metal vapor from dispersing out of a first reaction vessel,while a group-III nitride crystal is grown within the first reactionvessel using a mixed molten liquid which contains at least an alkalinemetal and a group-III metal and a nitrogen material brought from theoutside of the first reaction vessel.

[0118] By the crystal growth method according to the present invention,a mixed molten liquid which at least contains an alkaline metal and agroup-III metal is present in the first reaction vessel, and temperaturecontrol of this first reaction vessel is carried out so that crystalgrowth can be performed. A nitrogen material is brought from theexterior of this first reaction vessel, then, the alkaline metal,group-III metal, and nitrogen material react, and thus, a crystal of thegroup-III nitride grows. The nitrogen material means nitrogen molecules,nitrogen atoms, and/or nitrogen molecules and/or nitrogen atomsgenerated from a compound containing nitrogen.

[0119] In a temperature range in which a crystal of the group-IIInitride grows, the alkaline metal has a certain vapor pressure.According to the present invention, th thus-generated alkaline-metalvapor is prevented from dispersing out of the first reaction vessel.

[0120] In particular, in a first embodiment of the present invention, azone through which the nitrogen material passes in the first reactionvessel is prevented from being blocked by the alkaline-metal vapor,while a group-III nitride crystal is grown within the first reactionvessel using a mixed molten liquid which contains at least an alkalinemetal and a group-III metal, and a nitrogen material brought from theoutside of the first reaction vessel.

[0121] To prevent the zone through which the nitrogen material passes inthe first reaction vessel from being blocked by the alkaline-metal vapormay include not only to prevent the alkaline metal from condensing inthis zone but also to remove (mechanically) the alkaline metal condensedthere.

[0122] In order to prevent condensation of the alkaline metal, whengrowing the group-III nitride crystal in the first reaction vessel usingthe mixed molten liquid which contains the alkaline metal and group-IIImetal, and the nitrogen material brought from the outside of the firstreaction vessel, controlling is made such as to prevent the temperatureof a portion above the surface of the mixed molten liquid which containsthe group-III metal with the alkaline metal from decreasing from thetemperature below which the alkaline metal vapor may condense in thefirst embodiment. In this case, the temperature above the surface of themixed molten liquid in the first reaction vessel is not to be made lowerthan the temperature of the mixed molten liquid including the surface ofthe mixed molten liquid.

[0123]FIG. 5 shows a configuration of a crystal growth apparatus in thefirst embodiment of the present invention. In FIG. 5, in the firstreaction vessel 101, Na as the alkaline metal and a metal Ga as asubstance which contains a group-III metallic element at least arecontained, and they form a mixed molten liquid 102 at the temperaturerange in which a crystal of the group-III nitride crystal can grow.

[0124] There, the first reaction vessel 101 is made of a stainlesssteel, and, the space zone 103 of the first reaction vessel 101 isfilled by a nitrogen gas (N₂), as the substance which at least containsa nitrogen element. This nitrogen gas 103 can be supplied through anitrogen supply pipe 104 from the outside of the first reaction vessel101. In order to adjust the pressure of the nitrogen gas, a pressureadjustment mechanism 105 is provided. For example, a pressure sensor, apressure adjustment valve, etc. are included in this pressure adjustmentmechanism 105. This pressure adjustment mechanism 105 controls thepressure of the nitrogen gas in the first reaction vessel 101, forexample, to 50 atm.

[0125] Moreover, in the crystal growth apparatus shown in FIG. 5, afirst heating device 106 is provided in the outside of the firstreaction vessel 101 in a range of height in which the mixed moltenliquid 102 of the alkaline metal Na and group-III metal Ga is held suchthat the temperature of the mixed molten liquid 102 can be controlled sothat a crystal of the group-III nitride can grow inside or the surfaceof this mixed molten liquid 102.

[0126] Furthermore, in the crystal growth apparatus shown in FIG. 5, asecond heating device 107 is provided above the first heating device 106so that the temperature above the surface of mixed molten liquid 102 canbe controlled thereby.

[0127] Na which is the alkaline metal and Ga which is the group-IIImetal material can form the mixed molten liquid 102 as a result ofcontrol being made by the first heating device 106 into the temperature(for example, 750° C.) in which a crystal of the group-III nitridecrystal can grow. There, the temperature of the upper part of the firstreaction vessel 101 is controlled by the second heating device 107 sothat the temperature above the surface of the mixed molten liquid 102which includes Na which is the alkaline metal and Ga which is thegroup-III metal material is not less than the temperature of the mixedmolten liquid 102. In this state, a GaN crystal as the group-III nitrideis grown in the mixed molten liquid 108 and the surface 109 thereof, asGa which is the group-III metal is supplied from the mixed molten liquid102, and the growth temperature is thus maintained.

[0128] In the crystal growth apparatus shown in FIG. 5, inside 108 or inthe surface 109 of the mixed molten liquid 102 of Na and Ga, acontinuous growth of the GaN crystal is performed as the nitrogen gasand Ga react, or the nitrogen ingredient in the molten liquid suppliedfrom the nitrogen gas and Ga react, and thus, it is possible to obtain alarge size of the crystal.

[0129] Furthermore, in the crystal growth apparatus shown in FIG. 5,condensation of Na in the upper part of the first reaction vessel 101can be prevented as the temperature of the upper part of the firstreaction vessel 101 is controlled by the second heating device 107 sothat the temperature above the surface of the mixed molten liquid 102which includes Na which is the alkaline metal and Ga which is thegroup-III metal material may be not less than the temperature of themixed molten liquid 102 itself. That is, since the temperature above themixed molten liquid 102 is higher than the temperature of the mixedmolten liquid 102 itself, condensation of Na in the upper part of thefirst reaction vessel 101 can be prevented. Consequently, it becomespossible to prevent condensation of Na in the nitrogen supply pipe 104.That is, it is possible to prevent supply of the nitrogen gas from beingobstructed by condensation of Na in the nitrogen supply pipe 104.Moreover, the composition of the alkaline metal Na and the group-IIImetal Ga in the mixed molten liquid 102 is thus hardly changed, and,thus, stable crystal growth is attained. Thus, the alkaline metal(alkaline-metal vapor) Na is prevented from dispersing out of the firstreaction vessel 101 by preventing the alkaline-metal vapor from blockingthe nitrogen pipe 104 by properly heating the upper part of the reactionvessel 101.

[0130] In other words, when the temperature above the surface of themixed molten liquid 102 were lower than the temperature of the mixedmolten liquid 102, condensation of Na onto the inner wall of the firstreaction vessel 101 and/or the nitrogen supply pipe 104 might arise.Consequently, the composition of the alkaline metal Na and the group-IIImetal Ga in the mixed molten liquid 102 might change, or Na blocked thenitrogen supply pipe 104 so that the nitrogen could not be supplied. Inorder to avoid such a situation, the temperature of the upper part ofthe reaction vessel 101 is controlled by the second heating device 107so that the temperature above the surface of the mixed molten liquid 102should become more than the temperature of the mixed molten liquid 102itself according to the present invention.

[0131] Further, in the crystal growth apparatus shown in FIG. 6,temperature control of a more specific zone through which the nitrogenmaterial supplied externally passes into the first reaction vessel 101may be carried out.

[0132]FIG. 6 shows a crystal growth apparatus in a second embodiment ofthe present invention in which temperature control of a more specificzone through which the nitrogen material supplied externally passes intothe first reaction vessel 101 is performed.

[0133] That is, in the crystal growth apparatus shown in FIG. 6, inorder that temperature control of the zone (in this case, namely, thenitrogen supply pipe 104) through which the nitrogen material suppliedexternally passes into the first reaction vessel 101, a third heatingdevice 110 is provided in the outside of the nitrogen supply pipe 104.

[0134] In the crystal growth apparatus shown in FIG. 6, temperaturecontrol of the nitrogen supply pipe 104 is attained by the third heatingdevice 110. That is, as the nitrogen supply pipe 104 is directly heatedby the third heating device 110, the alkaline metal can be morepositively prevented from condensing in the nitrogen supply pipe 104more effectively than in the crystal growth apparatus shown in FIG. 5.Consequently, it becomes possible to bring nitrogen much more smoothlyinto the inside of the reaction vessel 101, and thus, more stablecrystal growth can be attained.

[0135] Thus, by the crystal growth apparatus shown in FIG. 6, thealkaline metal can be prevented from condensing to the more specificzone (nitrogen supply pipe 104) by heating this zone (nitrogen supplypipe 104) through which the nitrogen material supplied externally passesinto the first reaction vessel 101. Although the alkaline metal whichadheres to this zone (nitrogen supply pipe 104) may be removed (forexample, mechanically) instead of or in addition to preventingcondensation of the alkaline metal to the zone (nitrogen supply pipe104) through which nitrogen material passes as mentioned above, theconfiguration of the crystal growth apparatus shown in FIG. 6 canperform the same function in a simpler manner in consideration of theconfiguration of the apparatus. Moreover, even when the alkaline metalcondenses to the nitrogen supply pipe 104, it becomes possible tore-evaporate the thus-condensed alkaline metal by heating theabove-mentioned zone (nitrogen supply pipe 104), as the temperature ofthe zone (nitrogen supply pipe 104) through which the nitrogen materialsupplied externally passes can be controlled by the third heating device110.

[0136] Other than the configurations shown in FIGS. 5 and 6, it ispossible to realize the function of preventing the alkaline metal vaporfrom dispersing out of the first reaction vessel. For example, a secondreaction vessel is provided in the outside of the first reaction vessel,the nitrogen material is brought from the outside of the second reactionvessel, and a configuration is provided such that the alkaline metalvapor is prevented from dispersing out of the first reaction vesselwhile the first reaction vessel causes the nitrogen material suppliedfrom the second reaction vessel to pass inside therethrough.

[0137] In such a configuration, the nitrogen material is brought in thesecond reaction vessel from the outside. The mixed molten liquid whichcontains at least the alkaline metal and at least the group-III metal isprovided in the inside of the first reaction vessel, and the nitrogenmaterial passes inside through the first reaction vessel and thus isbrought into the first reaction vessel. Thereby, the alkaline metal,group-III metal and nitrogen material react in the first reactionvessel, and a crystal of the group-III nitride grows. In the temperaturerange in which a crystal of the group-III nitride grows, the alkalinemetal has a certain vapor pressure, and the thus-generated alkalinemetal vapor is prevented from dispersing out of the first reactionvessel.

[0138]FIG. 7 shows a crystal growth apparatus in a third embodiment ofthe present invention. In this configuration, a second reaction vessel111 is provided outside of a first reaction vessel 101, the nitrogenmaterial (in a form of gas) is supplied from the outside of the secondreaction vessel 111, the first reaction vessel 101 has a configurationsuch as to prevent the alkaline metal vapor from dispersing out of thefirst reaction vessel 101, while causes the nitrogen material providedfrom the second reaction vessel 111 to pass therethrough into the insideof the first reaction vessel 101. That is, in the crystal growthapparatus shown in FIG. 7, the second reaction vessel 111 is in theoutside of the first reaction vessel 101.

[0139] For the above-mentioned purpose, in the configuration of FIG. 7,a lid 112 is provided in the upper part of the first reaction vessel101. There, the material of the first reaction vessel 101 is BN (boronnitride), and the second reaction vessel 111 is made of stainless steel.

[0140] In the first reaction vessel 101, Na as the alkaline metal, and,a metal Ga as a substance at least containing the group-III metallicelement is contained. They form a mixed molten liquid 102 in thetemperature range in which a crystal of the group-III nitride grows. Thespace zone 103 in the first reaction vessel 101 and the space zone 113in the second reaction vessel 111 are filled by the nitrogen gas (N₂) asa substance which at least contains a nitrogen element. This nitrogengas can pass through the nitrogen supply pipe 104 pass, and thus can besupplied into the second reaction vessel 111 externally. Furthermore,there is a fine crevice between the first reaction vessel 101 and thelid 112 such as to allow the nitrogen gas to pass therethrough and thusto be supplied into the first reaction vessel 101 from the secondreaction vessel 111.

[0141] In addition, in order to adjust the nitrogen pressure, a pressureadjustment mechanism 105 is provided in the apparatus shown in FIG. 7.This mechanism includes, for example, a pressure sensor, a pressureadjustment valve, etc., and this pressure adjustment mechanism 105controls the nitrogen pressure in the second reaction vessel 111 and thefirst reaction vessel 101 into 50 atm., for example.

[0142] In the crystal growth apparatus shown in FIG. 7, a heating device116 is provided outside of the second reaction vessel 111 such that thetemperature inside of or in the surface of the mixed molten liquid 102in the first reaction vessel 101 can be controlled so that a crystal ofthe group-III nitride can grow therein.

[0143] The mixed molten liquid 102 of Na which is the alkaline metal,and Ga which is the group-III metal material is formed by performingtemperature control aiming at the temperature (for example, 750° C.) atwhich a crystal of the group-III nitride can grow. In this state, a GaNcrystal as a group-III nitride can grow in the mixed molten liquid 108and in the surface of the mixed molten liquid 109 as Ga which is thegroup-III metal is supplied by the mixed molten liquid, and theabove-mentioned growth temperature is maintained.

[0144] In the crystal growth apparatus shown in FIG. 7, in the mixturemolten liquid of Na and Ga 108, and in the surface thereof 109,continuous growth of the GaN crystal is achieved as the nitrogen gas andGa react or the nitrogen ingredient in the molten liquid supplied fromnitrogen gas and Ga react, and, thus, it becomes possible to obtain alarge size of the crystal.

[0145] Furthermore, in the crystal growth apparatus shown in FIG. 7, thealkaline metal can be prevented from dispersing out of the firstreaction vessel 101 almost completely as the first reaction vessel 101is provided with the lid 112. Thereby, change in the composition of thealkaline metal and group-III metal is well controlled, and it becomespossible to grow the group-III nitride crystal with well controlledcondition. At this time, condensation of the alkaline metal into thenitrogen supply pipe 104 can also be controlled (avoided).

[0146] Moreover, in controlling the temperature in the first reactionvessel 101 so that the temperature above the surface of the mixed moltenliquid 102 which consists of Na which is the alkaline metal, and Gawhich is the group-III metal material becomes more than the temperatureof the mixed molten liquid 102 itself as described above for the crystalgrowth apparatus shown in FIG. 5, it becomes possible to preventdispersion of the alkaline metal occurring due to condensation thereofin the supply pipe or the like externally from the mixed molten liquid102 more positively.

[0147] Moreover, in any of the configurations of the crystal growthapparatus shown in FIGS. 5, 6 and 7, the nitrogen material may insteadbe brought into the reaction vessel 101 or 111 horizontally of the firstreaction vessel or second reaction vessel 111, or from a direction belowthe horizontal direction thereof.

[0148]FIG. 8 shows a crystal growth apparatus in a fourth embodiment ofthe present invention. In this configuration, the nitrogen supply pipe104 is connected to the second reaction vessel 111 at the bottom of thecrystal growth apparatus, as shown in the figure. Therefore, thenitrogen gas which is a nitrogen material is supplied from the bottom ofthe second reaction vessel 111. The inventor of the present inventionconfirmed experimentally that an alkaline metal in a form of vapor wasmore likely to condense in an upper part of a reaction vessel than in alower part thereof. Therefore, the nitrogen supply pipe 104 can be morepositively prevented from being blocked by the alkaline metal and canbring the nitrogen gas toward the mixed molten liquid more positively,as the nitrogen is supplied from the bottom as in the crystal growthapparatus shown in FIG. 8. Consequently, it becomes possible to ensurebringing (provision) of the nitrogen gas into the mixed molten liquid,and, thereby, the control (control of the nitrogen pressure) of crystalgrowth can be performed more positively.

[0149] In addition, in the example of FIG. 8, although the nitrogen gasis brought inside from the bottom of the second reaction vessel 111, anembodiment of the present invention is not limited thereto, and similareffect can be obtained as long as the nitrogen gas is brought insidefrom a horizontal direction (as indicated by a broken line 104′ in FIG.8) or from a direction lower than the horizontal direction of the secondreaction vessel 111.

[0150] Moreover, although the crystal growth apparatus shown in FIG. 8is an example corresponding to the embodiment shown in FIG. 7, anexample corresponding to any of the configurations shown in FIGS. 5 and6 can be embodied in the same manner. That is, the nitrogen gas may bebrought horizontally into the first reaction vessel 101 or secondreaction vessel 111, or in a direction below the horizontal directionthereinto, there (as indicated by a broken line 104′ in FIG. 5).

[0151] In addition, in the above-described embodiments, although Na isused as a metal (alkaline metal) having a low melting point and a highvapor pressure, potassium (K) etc. can also be used instead of Na. Thatis, any alkaline metal may be used as long as, in the temperature rangein which a crystal of a group-III nitride can grow, it is in a form of amolten liquid.

[0152] Moreover, in the above-described embodiments, at least, as asubstance at least containing a group-III metallic element, Ga is used.However, another metal such as Al or In, a mixture thereof or an alloythereof may be used instead.

[0153] Moreover, although a nitrogen gas is used in the above-describedembodiments as a substance which at least contains a nitrogen element,another gas, such as NH₃, may also be used instead of the nitrogen gas.

[0154] Moreover, although the first reaction vessel 101 is made ofstainless steel in the above-described embodiments, any material can beused as the material of the first reaction vessel instead as long as itcan form a closed space separate from the exterior atmosphere, andresists the temperature and pressure needed for growing a group-IIInitride crystal, and, also, does not react with the alkaline metal, andthus is not melted as an impurity when the group-III nitride crystalgrows.

[0155] By employing the crystal growth apparatus in any of theabove-described first, second, third and fourth embodiments shown inFIGS. 5, 6, 7 and 8, for growing a group-III nitride crystal, such alarge-sized group-III nitride crystal as that can be put into practicein manufacture of semiconductor device can be obtained at low cost.

[0156] As an example of a method of growing a group-III nitride crystalaccording to the present invention, Ga is used as a group-III metal, anitrogen gas is used as a nitrogen material, Na is used as a flux, thetemperature of the reaction vessel and flux vessel is made into 750° C.,and the nitrogen pressure is fixed into 50 kg/cm². Thereby, a GaNcrystal can grow.

[0157] Moreover, by using a group-III nitride crystal thus grown up bythe growth method according to the present invention, a group-IIInitride semiconductor device can be produced.

[0158]FIG. 9 shows an example of configuration of such a semiconductordevice according to the present invention. The semiconductor deviceshown in FIG. 9 is in a form of a semiconductor laser. As shown in thefigure, in this semiconductor device, on an n-type GaN substrate 301using a group-III nitride crystal produced according to theabove-described crystal growth method according to the presentinvention, an n-type AlGaN clad layer 302, an n-type GaN guide layer303, an InGaN MQW (multiple quantum well) activity layer 304, a p-typeGaN guide layer 305, a p-type AlGaN clad layer 306, and a p-type GaNcontact layer 307 are formed one by one through crystal growthprocesses. As the crystal growth method therefor, a thin film crystalgrowth method, such as an MO-VPE (organometallic vapor phase epitaxy)method, an MBE (molecular beam epitaxy) method, or the like may be used.

[0159] Subsequently, a ridge structure is formed in the laminated filmsof GaN, AlGaN, and InGaN, SiO₂ insulating layer 308 is formed only witha hole formed as a contact region, a p-side ohmic electrode Au/Ni 309,and an n-side ohmic electrode Al/Ti 310 are respectively formed on topand bottom thereof, and thus, a semiconductor device (semiconductorlaser) shown in FIG. 9 is formed.

[0160] By injecting an electric current from the p-side ohmic electrodeAu/Ni 309 and n-side ohmic electrode Al/Ti 310 of this semiconductorlaser, it oscillates, and emits laser light in a direction of an arrow Ashown in FIG. 9.

[0161] Since the group-III nitride crystal (GaN crystal) according tothe present invention is used in this semiconductor laser as thesubstrate 301, there are few crystal defects in the semiconductor laserdevice, and it provides a large power output and has a long life.Moreover, since the GaN substrate 301 is of n type, an electrode 310 canbe formed directly onto the substrate 301, thus does not need to drawtwo electrodes of p side and n side only from the obverse surface as inthe prior art shown in FIG. 1, and, thus, cost reduction can beachieved.

[0162] Furthermore, in the semiconductor device shown in FIG. 9, itbecomes possible to form a light emitting end surface by cleavage, also,chip separation can be performed by cleavage. Thus, it is possible toachieve a high-quality semiconductor device at low cost.

[0163] With reference to FIGS. 10 through 15, a crystal growth method ina fifth embodiment and variant embodiments thereof, of the presentinvention for growing a group-III nitride crystal will now be described.

[0164] (First Feature of the Fifth Embodiment of the Present Invention)

[0165] In the crystal growth method in the fifth embodiment of thepresent invention, a crystal of a group-III nitride including agroup-III metal and nitrogen is grown in a reaction vessel from analkaline metal, a substance at least containing the group-III metal, anda substance at least containing the nitrogen. In particular, a growthprocess is made such that a growth condition is set in which the crystalgrowth stops after a growth condition is set by which a group-IIInitride crystal starts growing, and, then, the growth condition is setby which the crystal growth starts, again.

[0166] The alkaline metal, the substance which at least contains thegroup-III metal, and the substance which at least contains the nitrogenare present in the reaction vessel. They may be supplied externally, ormay be present in the reaction vessel originally. This reaction vesselis provided with a temperature control mechanism and a pressure controlmechanism, and, thereby, it is possible arbitrarily to raise thetemperature in the reaction vessel so as to enable crystal growththerein, raise the pressure in the reaction vessel so as to enablecrystal growth therein, lower the temperature in the reaction vessel soas to stop the crystal growth, to lower the pressure in the reactionvessel so as to stop the crystal growth, and to maintaintemperature/pressure in the reaction vessel for a desired time interval.

[0167] Then, by setting the temperature in the reaction vessel so as tocause it to satisfy the growth condition by which the group-III nitridecrystal can grow, crystal growth of the group-III nitride begins.Immediately after the crystal growth of the group-III nitride begins andthus nucleus generation starts, the condition in the reaction vessel ismade to enter a condition by which the crystal growth stops, and thusthe nucleus generating stops. Next, by returning the temperature of thereaction vessel to the condition by which the crystal growth startsagain, the crystal growth of the group-III nitride progresses utilizingthe nucleus generated before as a seed crystal.

[0168] The nitrogen material used the embodiment according to thepresent invention is a nitrogen molecule, a nitrogen in a form of atomand/or a nitrogen molecule, and/or a nitrogen molecule and/or a nitrogenin a form of atom generated from a compound containing nitrogen.

[0169] (Second Feature of the Fifth Embodiment of the Present Invention)

[0170] In addition to the above-described first feature, after settingand maintaining the temperature by which the crystal growth starts in azone in the reaction vessel in which the crystal of the group-IIInitride grows, the temperature in the reaction vessel is lowered so thatthe crystal growth stops and also the group-III metal and other metal donot form an alloy, and the thus-lowered temperature is maintained. Then,after that, the temperature in the reaction vessel is raised to thetemperature at which the crystal growth starts again.

[0171] An alkaline metal, a substance which at least contains agroup-III metal, and a substance which at least contains a nitrogen areprovided in the reaction vessel. They may be supplied externally or maybe provided in the reaction vessel originally. This reaction vessel isprovided with a unit for performing a temperature control function, and,thereby, the temperature in the reaction vessel is raised so thatcrystal growth may occur, is lowered so that the crystal growth maystop, or the temperature in the reaction vessel may be maintained for adesired time interval.

[0172] By raising the temperature in the reaction vessel so that thegroup-III nitride crystal may grow, crystal growth of the group-IIInitride begins. The nucleus generation stops by then lowering thetemperature in the reaction vessel so that the crystal growth stops,immediately after the crystal growth of the group-III nitride begins andnucleus generation starts. Next, by raising the temperature in thereaction vessel so that the crystal growth may start again, the crystalgrowth of the group-III nitride progresses by utilizing the nucleusgenerated before as a seed crystal.

[0173] (Third Feature of the Fifth Embodiment of the Present Invention)

[0174] In addition to the above-described second feature, the increaseand decrease of the temperature (growth temperature) in the reactionvessel are repeated. Thereby, crystal growth of the group-III nitrideprogresses by utilizing the crystal nucleus which has been finallygenerated as a seed crystal.

[0175] (Fourth Feature of the Fifth Embodiment of the Present Invention)

[0176] In addition to any one of the above-described second feature andthird feature, the substance which at least contains nitrogen is in aform of a gas, and a gas pressure of the gas is maintained during thecrystal growth.

[0177] The fifth embodiment of the present invention including theabove-described second, third and fourth features will now be describedwith reference to FIGS. 10 and 11. FIG. 10 shows a configuration of acrystal growth apparatus in the fifth embodiment of the presentinvention. FIG. 11 shows a temperature control sequence for the reactionvessel in the fifth embodiment.

[0178] A mixed molten liquid 1102 of Ga as the group-III metal and Na asthe flux is provided in the reaction vessel 1101, shown in FIG. 10. Inthe reaction vessel 1101, a heating device 1106 is provided such thatthe temperature in the reaction vessel 1101 is controlled so thatcrystal growth may occur. A nitrogen gas is used as the nitrogenmaterial. The nitrogen gas is supplied through a nitrogen supply pipe1104 into a space 1103 in the reaction vessel 1101 from the outside ofthe reaction vessel 1101. In order to adjust the nitrogen pressure atthis time, a pressure adjustment mechanism 1105 is provided. Thispressure adjustment mechanism 1105 includes a pressure sensor, apressure adjustment valve, etc. In this apparatus, a state by which thenitrogen gas is supplied to the reaction vessel at a fixed pressure canbe maintained thereby.

[0179] Under such a condition, the temperature in the reaction vessel iscaused to increase to a temperature T1 (for example, 750° C.) by whichthe crystal growth starts in a first process, as shown in a FIG. 11.Then, this condition is maintained for a predetermined time interval(for example, 30 minutes). Thereby, a nucleus of a GaN crystal which isa group-III nitride is generated in the reaction vessel 1101 shown inFIG. 10. Next, the temperature in the reaction vessel 1101 is lowered toa temperature T2 (for example, 400 degrees C.) at which the crystalgrowth stops. Next, the temperature in the reaction vessel 1101 iscaused to increase to the temperature T1 by which the crystal growthstarts again, and this condition is maintained for 30 minutes, and,then, the temperature in the reaction vessel 1101 is again lowered tothe temperature T2. A nucleus of the GaN crystal is again generated atthe time of this temperature increase.

[0180] Then, the temperature in the reaction vessel 1101 is againincreased to T1, and this temperature is maintained for a time such thata required crystal size may be obtained. At this time, the crystalgrowth progresses by utilizing the nucleus generated at the first twotimes of temperature increase, the GaN crystal becomes larger, and theGaN crystals 1107 and 1108 grow on the wall of the reaction vessel 1101and near a gas-liquid interface between the mixed molten liquid 1102 ofGa and Na and the space 1103 in the reaction vessel, as shown in FIG.10.

[0181] When a case where the temperature increase and decrease forcontrolling nucleus generation were performed according to the presentinvention and a case where such temperature control was not performed asin the prior art were experimentally compared, it was seen that, in thecase of controlling the temperature according to the present invention,nucleus generation could be controlled remarkably, and, thus, it becamepossible to obtain a large-sized crystal, and, thereby, the GaN crystalwhich could be used more practicality was obtained.

[0182] In this fifth embodiment of the present invention, although atemperature rise of the reaction vessel for nucleus generation sake, andtemperature descent are repeated twice, it is effective even byperforming only once the same. However, it becomes possible to generatea preferential crystal nucleus by performing the repetition. Inaddition, the nitrogen pressure at this time is 50 atm., and isremarkably low as compared with the pressure in the super-high-pressuremethod as in the above-mentioned second prior art.

[0183] (Fifth Feature of the Fifth Embodiment of the Present Invention)

[0184] In addition to the above-described fourth feature, additionalsupply of the substance which at least contains the group-III metal ismade at the time the temperature is low.

[0185] A first variant embodiment of the above-described fifthembodiment of the present invention will now be described with referenceto FIGS. 12 and 13. FIG. 12 shows a elevational sectional view of acrystal growth apparatus in the first variant embodiment of the fifthembodiment of the present invention, and FIG. 13 shows a temperaturecontrol sequence for the reaction vessel of the apparatus shown in FIG.12.

[0186] In addition to the configuration shown in FIG. 10, a unit ofperforming the additional supply of the group-III metal is provided inthe configuration as shown in FIG. 12. Only the unit which carries outthe additional supply of the group-III metal is the difference from theconfiguration shown in FIG. 10 and will now be described.

[0187] A metal Ga is used as the group-III metal, and in order to carryout the additional supply of the metal Ga, a group-III metal supply pipe1310 is provided. At an projection end of the group-III metal supplypipe 1310, the metal Ga 1309 for the additional supply is held in a formof powder. This inner projection end of this the group-III metal supplypipe 310 has a hole 1311. The opposite outer end of the group-III metalsupply pipe 1310 projects out of the reaction vessel 1301, and, byapplying a nitrogen pressure from this end, the metal Ga 1309 at theinner end of the group-III metal supply pipe 310 is supplied to themixed molten liquid 1302 through the hole 1311.

[0188] In this configuration, the temperature in the reaction vessel1301 is increased to the temperature T1 (for example, 750° C.) at whichthe crystal growth starts at a first process as shown in FIG. 13. Then,this state is maintained for a predetermined time interval (for example,30 minutes), thereby, a nucleus of a GaN crystal which is the group-IIInitride is generated in the reaction vessel 1301 shown in FIG. 12. Next,the temperature in the reaction vessel 1301 is lowered to thetemperature T2 (for example, 400 degrees C.) at which the crystal growthstops. Then, the temperature in the reaction vessel 1301 is increased toT1 again, and this temperature is maintained for a time interval suchthat a certain crystal size is obtained. At this time, the crystalgrowth progresses utilizing the nucleus generated at the time of thefirst temperature increase, the GaN crystal becomes larger, and the GaNcrystal 1307 and the GaN crystal 1308 grow on the wall of the reactionvessel 1301 and near the gas-liquid interface between the mixed moltenliquid 1302 of Ga and Na and the space 1303 in the reaction vessel 1301.

[0189] As mentioned above, the nitrogen gas which is the nitrogenmaterial can be supplied to the reaction vessel 1301 from the outsidecontinuously at the fixed pressure, and, thereby, the nitrogen is notexhausted. However, Ga which is the group-III metal material may beexhausted as the GaN crystal grows, or, the ratio with Na which is theflux may be changed even when the exhaustion does not actually occur.Thereby, a growth parameter may be changed gradually, the crystalquality may be changed, and, thus, it may become difficult to maintainstable crystal growth.

[0190] Then, after the crystal growth progresses to some extent, thetemperature in the reaction vessel 1301 is lowered to a temperature atwhich the crystal growth stops, and, thus, it becomes possible tocontrol the quantity ratio of the group-III metal and Na flux bycarrying out the additional supply of the Ga metal, as shown in FIG. 13.Consequently, stable growth of the GaN crystal is attained, and itbecomes possible to obtain the high-quality crystal having few defects.

[0191] Furthermore, fluctuation in the crystal growth can be wellcontrolled by carrying out additional supply of the Ga at a timing atwhich the crystal growth does not progress (temperature is low), and itbecomes possible to grow up a high-quality GaN crystal.

[0192] (Sixth Feature of the Fifth Embodiment of the Present Invention)

[0193] In addition to the above-described first feature, the substancewhich at least contains nitrogen is in a form of a gas, after settingand maintaining the effective nitrogen pressure in a zone where thegroup-III nitride crystal grows to a pressure at which crystal growthstarts, the effective nitrogen pressure is then lowered to a pressure atwhich the crystal growth stops, and the thus-lowered pressure ismaintained. Then, after that, the above-mentioned effective nitrogenpressure is increased to the effective nitrogen pressure at which thecrystal growth starts again.

[0194] The alkaline metal, the substance which at least contains thegroup-III metal, and the substance which at least contains the nitrogenare provided in the reaction vessel. They may be supplied from theoutside or may be provided in the reaction vessel originally.

[0195] A pressure control mechanism (1105 shown in FIG. 10) is providedin this reaction vessel, and, thereby, raising the effective nitrogenpressure to the pressure at which crystal growth may occur, lowering thepressure to a pressure at which the crystal growth may stop, andmaintaining each pressure for a desired time interval can be performed.

[0196] In this configuration, by raising the effective nitrogen pressurein the reaction vessel to the pressure at which the group-III nitridecrystal may grow, crystal growth of the group-III nitride begins. Then,the crystal-nucleus generation stops by lowering the effective nitrogenpressure in the reaction vessel to the pressure at which the crystalgrowth stops immediately after the crystal growth of the group-IIInitride begins and thus crystal nucleus generation starts. Next, byraising the effective nitrogen pressure in the reaction vessel to thepressure at which the crystal growth starts again, crystal growth of thegroup-III nitride progresses by utilizing the nucleus generated beforeas a seed crystal.

[0197] (Seventh Feature of the Fifth Embodiment of the PresentInvention)

[0198] In addition to the above-described sixth feature, increase anddecrease of the effective nitrogen pressure are performed several times.

[0199] By repeating the increase and decrease of the effective nitrogenpressure according to the above-described sixth feature, crystal growthof the group-III nitride progresses by utilizing the crystal nucleuswhich has been finally obtained by the nucleus generation as a seedcrystal.

[0200] A second variant embodiment of the fifth embodiment having theabove-described sixth and seventh features will now be described withreference to FIG. 14. In this variant embodiment, the crystal growthapparatus shown in FIG. 10 is used.

[0201] The mixed molten liquid 1102 of Ga as the group-III metal and Naas the flux is provided in the reaction vessel 1101. In the reactionvessel 1101, a heating device 1106 is provided so that it can controlthe temperature in the reaction vessel 1101 to the temperature at whichcrystal growth may occur. Nitrogen gas is used as the nitrogen material.The nitrogen gas is supplied through a nitrogen supply pipe 1104, and issupplied to a space 1103 in the reaction vessel 1101 from the outside ofthe reaction vessel 1101. In order to adjust the nitrogen pressure atthis time, a pressure adjustment mechanism 1105 is provided. Thispressure adjustment mechanism 1105 includes a pressure sensor, apressure adjustment valve, etc.

[0202] In this configuration, the nitrogen pressure in the reactionvessel 1101 is raised to a pressure P1 (for example, 50 atm.) at whichcrystal growth may start, at a first process as shown in FIG. 14. Thisstate is maintained for a predetermined time interval (for example, 30minutes), then, a nucleus of a GaN crystal which is the group IIInitride is generated in the reaction vessel 1101. Next, the nitrogenpressure in the reaction vessel 1101 is lowered to a pressure P2 (forexample, 10 atm.) at which the crystal growth stops. Next, afterincreasing the nitrogen pressure in the reaction vessel 1101 to theabove-mentioned pressure P1 again, this state is maintained for 30minutes. Then, after that, the nitrogen pressure in the reaction vessel1101 is again lowered to the above-mentioned pressure P2. The nucleus ofthe GaN crystal is generated again at the time of this pressureincrease.

[0203] Then, the nitrogen pressure in the reaction vessel 1101 isincreased to the pressure P1, and, then, the thus-raised pressure ismaintained till such a time has elapsed that a required crystal size isobtained. At this time, the crystal growth progresses by utilizing thenucleus generated through the first two times of pressure increase, theGaN crystal becomes larger, and the GaN crystals 1107 and 1108 grow onthe wall of the reaction vessel 1101 and near the gas-liquid interfacebetween the mixed molten liquid 1102 of Ga and Na and the space zone1103 in the reaction vessel 1101.

[0204] When a case where pressure increase and decrease of the nitrogenpressure for controlling nucleus generation according to the presentinvention was performed and a case where such a pressure control forcontrolling nucleus generation was not performed as in theabove-mentioned prior art were experimentally compared, nucleusgeneration was greatly controlled (the number of nucleuses generatedcould be effectively reduced) in the case where the pressure control forcontrolling nucleus generation was performed according to the presentinvention. Consequently, it became possible to enlarge the crystal sizeand thus the GaN crystal which can be used more practically could beobtained.

[0205] In this embodiment, although increase and decrease of thenitrogen pressure in the reaction vessel for the purpose of controllingnucleus generation are repeated twice, a similar effect can be obtainedeven the same operation is performed only once. It becomes possible togenerate a preferential crystal nucleus as this pressure increase anddecrease operation is repeated. In addition, the required temperature inthe reaction vessel at this time is 750 degrees C., and is remarkablylow as compared with the temperature in the super-high-pressure methodwhich is the above-described second prior art.

[0206] (Eighth Feature of the Fifth Embodiment of the Present Invention)

[0207] In addition to the above-described seventh feature, additionalsupply of the substance which at least contains the group-III metal isperformed at the time the effective nitrogen pressure is lowered.

[0208] A third variant embodiment of the fifth embodiment of the presentinvention having the abovementioned eighth feature will now be describedwith reference to FIG. 15. The crystal growth apparatus shown in FIG. 12is used in the third variant embodiment of the fifth embodiment. FIG. 15shows a pressure control sequence of the reaction vessel in thisembodiment.

[0209] The nitrogen pressure in the reaction vessel 1301 is raised tothe pressure P1 (for example, 50 atm.) at which crystal growth starts,in a first process. This state is maintained for a predetermined timeinterval (for example, 30 minutes), and, then, a nucleus of a GaNcrystal which is the group-III nitride is generated in the reactionvessel 1301. Next, the nitrogen pressure in the reaction vessel 1301 islowered to the pressure P2 (for example, 10 atm.) at which the crystalgrowth stops. Then, the nitrogen pressure in the reaction vessel 1301 israised to the above-mentioned pressure P1 again, and this pressure ismaintained till such a time interval has elapsed that a certain crystalsize is obtained. At this time, the crystal growth progresses utilizingthe nucleus generated at the time of the first pressure increase, theGaN crystal thus becomes larger, and the GaN crystal 1307 and the GaNcrystal 1308 grow on the wall of the reaction vessel 1301 and near thegas-liquid interface between the mixed molten liquid 1302 of Ga and Naand the space 1303 in the reaction vessel 1301.

[0210] As described above, the nitrogen gas which is the nitrogenmaterial can be supplied from the outside, and the nitrogen thus is notexhausted. However, Ga which is the group-III metal material may beexhausted as the GaN crystal growth progresses, or, the ratio thereofwith the flux (Na) may be changed even when Ga is not actuallyexhausted. Thereby, a growth parameter may be changed gradually, andthus, the crystal quality may be changed and it may become difficult tomaintain stable crystal growth.

[0211] Then, after the crystal growth progresses to some extent, thepressure of the nitrogen in the reaction vessel is lowered to thepressure at which the crystal growth stops, and, thereby, it becomespossible to control the quantity ratio of the group-III metal and the Naflux by carrying out additional supply of the Ga metal, as shown in FIG.15. Consequently, stable crystal growth of the GaN crystal is attainedand it becomes possible to obtain a high-quality crystal having fewdefects.

[0212] Furthermore, fluctuation in the crystal growth can be wellcontrolled by carrying out additional supply of the Ga at a timing atwhich the crystal growth does not progress, and, thus, it becomespossible to grow up a high-quality GaN crystal.

[0213] A crystal growth apparatus such that crystal growth is performedthereby according to the crystal growth method having any of theabove-described first through eighth features of the fifth embodiment ofthe present invention is included in the scope of the present invention.

[0214] Furthermore, a group-III nitride crystal obtained through thecrystal growth method having the any of the above-described firstthrough eighth features of the fifth embodiment of the presentinvention, and/or the above-mentioned crystal growth apparatus isincluded in the scope of the present invention.

[0215] A group-III nitride crystal semiconductor device produced byusing the above-mentioned group-III nitride crystal is also included inthe scope of the present invention.

[0216] An embodiment of a semiconductor laser to which theabove-mentioned semiconductor device is applied is shown in FIG. 9, and,is the same as that already described above with reference FIG. 9.

[0217] Also in this case, as described above, since a group-III nitridecrystal (GaN crystal) according to the present invention is used in thissemiconductor laser as the substrate 301, there are few crystal defectsin the semiconductor laser, and, thus, it provides a large power outputand has a long life. Moreover, since the GaN substrate 301 is of n type,an electrode 310 can be formed directly in the substrate 301, thus doesnot need to draw two electrodes of p side and n side only from theobverse surface as in the prior art shown in FIG. 1, and, thus, costreduction can be achieved.

[0218] Furthermore, in the semiconductor device shown in FIG. 9, itbecomes possible to form a light emitting end surface by cleavage, also,chip separation can be performed by cleavage. Thus, it is possible toachieve a high-quality semiconductor device at low cost.

[0219] Hereafter, a sixth embodiment of the present invention will nowbe described with reference to figures. In the sixth embodiment of thepresent invention, a mixed molten liquid of an alkaline metal and asubstance which at least contains a group-III metal is provided in areaction vessel. When carrying out crystal growth of the group-IIInitride including the group-III metal and nitrogen from the mixed moltenliquid and a substance which at least contains nitrogen, a localconcentration distribution (or concentration unevenness) of dissolvednitrogen is intentionally created in the mixed molten liquid.

[0220] There, the local concentration distribution of dissolved nitrogencan be produced in the mixed molten liquid by a specific shape of avessel holding the mixed molten liquid therein.

[0221] A growth method for group-III nitride crystal in the sixthembodiment of the present invention will now be described in detail. Ina reaction vessel, an alkaline metal, a substance which at leastcontains a group-III metal, and a substance which at least containsnitrogen is provided. These materials may be supplied from the outsideor may be made to be provided in the reaction vessel originally. Atemperature control mechanism is prepared in this reaction vessel, and,thereby, raising the temperature inside of the reaction vessel to atemperature at which crystal growth may occur, lowering the temperaturein the reaction vessel to a temperature at which the crystal growth maystop, and maintaining any one of the above-mentioned temperatures in thereaction vessel for a desired time interval can be performed. By thussetting the temperature in the reaction vessel, and the effectivenitrogen partial pressure to the conditions by which an group-IIInitride crystal may grow, it is possible to make crystal growth of thegroup-III nitride start.

[0222] When a predetermined temperature is set by the above-mentionedtemperature control mechanism, the alkaline metal and the substancewhich at least contains the group-III metal form a mixed molten liquid.Nitrogen is then dissolved in this mixed molten liquid. There, the term‘dissolving’ means that the nitrogen is present in the mixed moltenliquid in a dissolved form.

[0223] The concentration of the dissolved nitrogen in the mixed moltenliquid is made to have a spatial (local) distribution (spatialunevenness) in this stage in the sixth embodiment of the presentinvention. It can be considered that the nitrogen moves towards theinside of the mixed molten liquid from the surface of the mixed moltenliquid under a predetermined temperature in a mixed molten liquidholding vessel, and, thereby, a local concentration distribution of thedissolved nitrogen in the mixed molten liquid occurs due to a specificshape of the mixed molten liquid holding vessel which will be describedlater.

[0224] Then, it becomes possible to grow up a crystal of the group-IIInitride in a specific zone of the mixed molten liquid by producing sucha local concentration distribution of the dissolved nitrogen in themixed molten liquid. That is, a crystal nucleus is generated at the timein an early stage of crystal growth beginning, and, when the dissolvednitrogen concentration in the mixed molten liquid has a localdistribution (unevenness), generation of crystal nucleuses may belimited to a specific zone of the mixed molten liquid accordingly. Then,each crystal nucleus act as a seed crystal, and crystal growth of thegroup-III nitride progresses therefrom.

[0225] Then, after the crystal growth progresses so that a predeterminedsize of crystal may be obtained thereby, the temperature in the reactionvessel is lowered to such a temperature that the crystal may be takenout from the reaction vessel.

[0226] There, the nitrogen mentioned above and below means nitrogenmolecules and nitrogen atoms produced from a compound containingnitrogen molecules or nitrogen, and, groups of atoms and groups ofmolecules containing nitrogen.

[0227] As described above, in the sixth embodiment of the presentinvention, a local concentration distribution of dissolved nitrogen isproduced in the mixed molten liquid by an inner shape of a mixed moltenliquid holding vessel holding the mixed molten liquid therein.

[0228]FIG. 16 shows an example of a configuration of a crystal growthapparatus in the sixth embodiment of the present invention. An alkalinemetal and a substance which at least contains a group-III metal (forexample, Ga) form a mixed molten liquid in a reaction vessel, and thecrystal growth apparatus in the sixth embodiment of the presentinvention is configured such that growth of crystals of group-IIInitride which includes the group-III metal and nitrogen may be carriedout from this mixed molten liquid and the substance which at leastcontains the nitrogen (N).

[0229] That is, with reference to FIG. 16, the mixed molten liquidholding vessel 2102 is set in the reaction vessel 2101. There, thematerial of the mixed molten liquid holding vessel 2102 is BN (boronnitride). Further, the mixed molten liquid holding vessel 2102 holds themixed molten liquid 2103 including the group-III metal (for example, Ga)and the alkaline metal (for example, Na).

[0230] Moreover, with reference to FIG. 16, a heating device 2106 isprovided in the reaction vessel 2101 such that the inside of thereaction vessel 2101 can be controlled to have a temperature at whichcrystal growth may occur. Moreover, a nitrogen supply pipe 2104 isprovided such as to supply a nitrogen gas to a space zone 2108 of thereaction vessel 2101 from the outside of the reaction vessel 2101, and,in order to adjust the nitrogen pressure in the reaction vessel 2101, apressure adjustment mechanism 2105 is provided. This nitrogen pressureadjustment mechanism 2105 includes a pressure sensor, a pressureadjustment valve, etc.

[0231] According to the sixth embodiment of the present invention, themixed molten liquid holding vessel 2102 has an inner shape such as tocreate a local concentration distribution of dissolved nitrogen in themixed molten liquid.

[0232]FIG. 17 shows an elevational sectional view of one example of themixed molten liquid holding vessel 2102 shown in FIG. 16. The mixedmolten liquid holding vessel 2102 shown in FIG. 17 has an inner wall2102 a shaped such that the inner volume (cross sectional area) becomessmaller toward the bottom thereof. That is, the shape of the inner wall2102 a of the mixed molten liquid holding vessel 2102 is a conic shapeor a pyramid shape having the pointed vertex thereof directed toward thebottom. That is, in the example shown in FIG. 17, the mixed moltenliquid 2103 is held at a portion surrounded by the inner wall 2102 ahaving the shape obtained from being shaved off into a conic shapehaving the vertex directed to the bottom.

[0233] In the crystal growth apparatus having the configuration shown inFIGS. 16 and 17, the nitrogen pressure in the reaction vessel 2101 ismade into 50 atm., and the temperature therein is increased to thetemperature of 750 degrees C. by which crystal growth starts. Bymaintaining this growth condition for a predetermined time interval, agroup-III nitride crystal (for example, GaN crystal) 2109 grows in themixed molten liquid holding vessel 2102. A nucleus of the group-IIInitride crystal (for example, GaN crystal) 2109 is generated and thecrystal growth progresses therefrom at the earlier stage of the crystalgrowth, and, a zone in which the group-III nitride crystal (for example,GaN crystal) 2109 grows is only an upper part of the mixed molten liquidholding vessel 2102 where the inner wall 2102 a is inclined as shown inFIG. 17.

[0234] If the shape of the inner wall 2102 a of the mixed molten liquidholding vessel 2102 did not have the shape shown in FIG. 17 (conic shapeor pyramid shape) but a pillar shape (cylinder) or a square pillar shape(prism), nucleuses of the group-III nitride crystal (for example, GaNcrystal) 2109 would grow all over the inner wall 2102 a of the mixedmolten liquid holding vessel 2102, and the group-III nitride crystal(for example, GaN crystal) 2109 in monocrystal would not become largerenough. In contrast thereto, when the shape of the inner wall 2102 a ofthe mixed molten liquid holding vessel 2102 is such as that shown inFIG. 17, nucleus generation of the group-III nitride crystal (forexample, GaN crystal) 2109 is limited to occur in a specific zone of themixed molten liquid 2103, it becomes possible to efficiently utilize thegroup-III metal (for example, Ga) in the mixed molten liquid 2103 forthe growth of the group-III nitride monocrystal (for example, GaN singlecrystal), and, thus, it becomes possible to obtain a large size of thecrystal.

[0235] It can be considered that such a behavior occurs due to thefollowing mechanism: That is, the nitrogen from the nitrogen gas bywhich the space zone 2108 of the reaction vessel 2101 is filled up isdissolved into the mixed molten liquid 2103 from the surface 2103 a ofthe mixed molten liquid 2103 (it moves by dispersion into a deeper partof the mixed molten liquid 103 from the surface 2103 a of the mixedmolten liquid 2103). When the shape of the inner wall 2102 a of themixed molten liquid holding vessel 2102 is such as that shown in FIG.17, the cross sectional shape of the inner wall 2102 a of the mixedmolten liquid holding vessel 2102 along a direction perpendicular to thedirection in which the nitrogen moves in the mixed molten liquid 2103 tothe inside of the mixed molten liquid 2103 by dispersion from thesurface 2103 a of the mixed molten liquid 2103 (namely, along thedirection from the top to the bottom) is changed. Thereby, the dissolvednitrogen concentration in the inside of the mixed molten liquid 2103 hasa spatial difference (distribution), and, thus, the crystal nucleus ofthe group-III nitride crystal (for example, GaN crystal) 2109 isgenerated in the above-mentioned specific part of inner wall 2102 a ofthe mixed molten liquid holding vessel 2102.

[0236] That is, when the cross sectional area of the inner wall 2102 aof the mixed molten liquid holding vessel 2102 is changed (when thecross sectional area of the mixed molten liquid 103 is changed by theshape of the inner wall 2102 a of the vessel 2102), the localdistribution (unevenness) of the dissolved nitrogen concentration arisesin the mixed molten liquid 2103. Consequently, generation of crystalnucleuses of the group-III nitride crystal (for example, GaN crystal)2109 occurs in a limited part in the mixed molten liquid 2103. Growth ofthe group-III nitride crystal (for example, GaN crystal) 2109 progressesfurther from the generated crystal nucleus, and, thus, the crystalgrowth progresses more preferentially from a crystal nucleus alreadygenerated once than in a zone in which no crystal nucleus is present. Atthis time, the temperature of the mixed molten liquid holding vessel2102 and the mixed molten liquid 2103 of the inside thereof is uniform.Therefore, from the surface 2103 a of the mixed molten liquid 2103, thenitrogen used as a group-V material for the group-III nitride crystal(for example, GaN crystal) 2109 moves by dispersion, and is consumed incrystal nucleuses of the III group-III nitride crystal (for example, GaNcrystal) 2109. Consequently, the group-III nitride crystal (for example,GaN crystal) 2109 grows up only in the specific part of the inner wall2102 a of the mixed molten liquid holding vessel 2102, and, thereby,growth of the group-III nitride crystal 2109 into a large size ofcrystal (for example, GaN crystal) is attained.

[0237]FIG. 18 shows a second example of the mixed molten liquid holdingvessel 2102 in the sixth embodiment of the present invention. In theexample shown in FIG. 18, the mixed molten liquid holding vessel 2102has a configuration such that a projection 2126 is formed from the innerwall 2102 a of the mixed molten liquid holding vessel 2102 at a level(height) below the surface 2103 a of the mixed molten liquid 2103.

[0238] When growing up the group-III nitride crystal (for example, GaNcrystal) 2109 using the mixed molten liquid holding vessel 2102 shown inFIG. 18, a nucleus of the group-III nitride crystal (for example, GaNcrystal) 2109 is generated centering near the projection end of theprojection 2126 of the inner wall 2102 a of the mixed molten liquidholding vessel 2102. Generation of the nucleus of the group-III nitridecrystal (for example, GaN crystal) 2109 occurs mainly near theprojection end of the projection 2126 in the mixed molten liquid 103.Thereby, the crystal nucleus at this location is mainly used forprogress of growth of the group-III nitride crystal (for example, GaNcrystal) 2109, and, thus, it becomes possible to grow up a large-sizedcrystal.

[0239] In the crystal growth apparatus having the configuration shown inFIGS. 16 and 18, the nitrogen pressure in the reaction vessel 2101 ismade into 50 atm., and the temperature therein is increased to thetemperature of 750 degrees C. at which crystal growth starts. Bymaintaining this growth condition for a predetermined time interval, thegroup-III nitride crystal (for example, GaN crystal) 2109 grows in themixed molten liquid holding vessel 2102. At this time, a nucleus of thegroup-III nitride crystal (for example, GaN crystal) 2109 is generatedand crystal growth progresses therefrom in the earlier stage of crystalgrowth, and the zone at which the group-III nitride crystal (forexample, GaN crystal) 2109 grows is limited to only a zone near theprojection end of the projection 2126 of the inner wall 2102 a of themixed molten liquid holding vessel 2102 as shown in FIG. 18.

[0240] It can be considered that such a behavior occurs by the followingmechanism: Namely, in the reaction vessel 2101, nitrogen from thenitrogen gas by which the space zone 2108 is filled is dissolved intothe mixed molten liquid 2103 from the surface 2103 a of the mixed moltenliquid 2103 (it moves by dispersion into the mixed molten liquid 2103deeper from the surface 2103 a of the mixed molten liquid 2103). In thecase of the example shown in FIG. 18, the cross sectional area insidethe mixed molten liquid holding vessel 2102 along the directionperpendicular to the direction of movement of the nitrogen in the mixedmolten liquid 103 is changed by the projection 2126 formed from theinner wall 2102 a of the mixed molten liquid holding vessel 2102.Thereby, the concentration of the dissolved nitrogen in the mixed moltenliquid 2103 has a spatial difference/unevenness (distribution), and thecrystal nucleus of the group-III nitride crystal (for example, GaNcrystal) 2109 is generated centering in the neighborhood of theprojection 2126. In this time, growth of the group-III nitride crystal(for example, GaN crystal) 2109 progresses further from the generatedcrystal nucleus, and thus, the crystal growth progresses morepreferentially from the crystal nucleus already generated than in a zonein which no crystal nucleus is present. At this time, the temperature inthe mixed molten liquid holding vessel 2102 and the mixed molten liquid2103 of the inside thereof is uniform. Thereby, from the surface 2103 aof the mixed molten liquid 2103, the nitrogen used as the group-Vmaterial for the group-III nitride crystal (for example, GaN crystal)2109 moves by dispersion, and is consumed in the crystal nucleus of thegroup-III nitride crystal (for example, GaN crystal) 2109. Consequently,the group-III nitride crystal (for example, GaN crystal) 2109 grows uponly in the specific part on the inner wall 102 a of the mixed moltenliquid holding vessel 2102, and, thus, growth of the group-III nitridecrystal 2109 into a large-sized crystal (for example, GaN crystal) isattained.

[0241] In the example of FIG. 18, the projection 2126 is formed from theinner wall 2102 a of the mixed molten liquid holding vessel 2102.However, a measure may be provided instead of provision of such aprojection. Namely, the mixed molten liquid holding vessel 2102 shouldhave a certain portion at which the cross sectional area is changed inthe inner wall 2102 a.

[0242]FIG. 19 shows a configuration of a crystal growth apparatus in aseventh embodiment of the present invention. In FIG. 19, the samereference numerals as those of FIG. 16 are given to correspondingparts/components. In the crystal growth apparatus shown in FIG. 19, afirst heating device 2116 and a second heating device 2117 are providedsuch that the group-III nitride crystal (for example, GaN crystal) 2109in the reaction vessel 2101 can be controlled to have a temperature bywhich crystal growth may occur. There, temperature control can beperformed individually by the first heating device 2116 and the secondheating device 2117.

[0243]FIG. 20A shows another example of the mixed molten liquid holdingvessel 2102, and the mixed molten liquid holding vessel 2102 shown inFIG. 20A is used in the crystal growth apparatus shown in FIG. 19. Withreference to FIG. 20A, this mixed molten liquid holding vessel 2102 hasan upper inner wall 2102 a and a lower inner wall 2102 b. The upperinner wall 2102 a has an inner volume (cross sectional area) becomingsmaller toward the bottom, while the lower inner wall 2102 b has auniform cross sectional area. That is, the three-dimensional shape ofthe inner wall of the mixed molten liquid holding vessel 2102 shown inFIG. 20A is such that a cone having a vertex directed downward istruncated, and, then, from the thus-produced bottom end plane thereof, acylindrical shape extends downward further.

[0244] In the crystal growth apparatus having the configuration shown inFIGS. 19 and 20A, nitrogen pressure in the reaction vessel 2101 is madeinto 50 atm., and the temperature therein at the upper part (2102 a) ofthe mixed molten liquid holding vessel 2102 is increased by the firstheating device 2116 to a temperature of 750 degrees C. at which crystalgrowth may start. The temperature of the lower part (2102 b) of themixed molten liquid holding vessel 2102 is made into 780 degrees C. bythe second heating device 2117. By maintaining this growth condition fora predetermined time interval, the group-III nitride crystal (forexample, GaN crystal) 2109 grows in the mixed molten liquid holdingvessel 2102. In this time, a nucleus of the group-III nitride crystal(for example, GaN crystal) 109 is generated, and crystal growthprogresses in the earlier stage of the crystal growth therefrom, andonly in the upper part, the group-III nitride crystal (for example, GaNcrystal) 2109 grows in which the inner wall of the mixed molten liquidholding vessel 2102 is inclined as shown in FIG. 20A (only in thespecific part on the upper inner wall 2102 a).

[0245] The crystal nucleus 2109 of the group-III nitride crystal (forexample, GaN crystal) is generated only in the specific part on theupper inner wall 2102 a of the mixed molten liquid holding vessel 2102same as in the example shown in FIG. 17. However, differently from theexample shown in FIG. 17, the inner wall of the mixed molten liquidholding vessel 2102 has the cylindrical lower part 2102 b in which thecross sectional area is uniform, in the mixed molten liquid holdingvessel shown in FIG. 20A. As mentioned above, when the inner wall of themixed molten liquid holding vessel were like a cylinder or a prism,nucleuses of the group-III nitride crystal (for example, GaN crystal)2109 would grow all over the inner wall of the mixed molten liquidholding vessel, and the group-III nitride crystal (for example, GaNcrystal) 2109 in monocrystal thus could not have a large size. When themixed molten liquid holding vessel is shaped as shown in FIG. 20A,nucleus generation is limited to effectively occur only in the specificzone, the group-III metal in the mixed molten liquid (for example, Ga)can thus be efficiently used for the growth of the group-III nitridemonocrystal (for example, GaN single crystal) 2109 from the nucleus thusgenerated in the limited zone, and thereby, a large-sized crystal can beobtained therefrom. Furthermore, in the configuration shown in FIG. 20A,the cross sectional area of the inner wall of the mixed molten liquidholding vessel 2102 becomes uniform below the mid height thereof. Thatis, the lower inner wall 2102 b has the uniform cross sectional area.Thereby, growth of the group-III nitride crystal (for example, GaNcrystal) 2109 is controlled there, but the mixed molten liquid whichincludes the group-III metal (Ga) and the alkaline metal (for example,Na) is kept. Thereby, the zone of the lower inner wall 2102 b acts as azone for keeping the group-III metal (for example, Ga) for the group-IIInitride crystal (for example, GaN crystal) 2109, and, thereby, thegroup-III metal (for example, Ga) can be continuously suppliedtherefrom, and the crystal can thus be grown up continuously to asufficient size.

[0246] Furthermore, in the crystal growth apparatus shown in FIGS. 19and 20A, a convection arises in the mixed molten liquid 2103 becausethere is a difference in temperature between the upper part and thelower part of the mixed molten liquid holding vessel 2102 as mentionedabove. The group-III metal (for example, Ga) is supplied from the lowerpart of the mixed molten liquid holding vessel 2102 by this convection,and the nitrogen which is the group-V material is supplied from the top,and, thus, efficient crystal growth is attained.

[0247] In addition, in the example of the crystal growth apparatus shownin FIG. 20A, although the shape of the inner wall of the mixed moltenliquid holding vessel 2102 is such that, first, the cross sectional areathereof becomes smaller downward, and, then, is uniform from the middlethereof as mentioned above, the shape of the inner wall of the mixedmolten liquid holding vessel 2102 may be such that, as shown in FIG.20B, first, the cross sectional area may become smaller downward, and,then, from the middle height thereof, it may become larger downward(like a tsuzumi or Japanese hand drum).

[0248] Moreover, the inner shape of the mixed molten liquid holdingvessel 2102 is not necessarily limited to any one of those shown inFIGS. 17, 18, 20A and 20B, but, should just be a shape such that,thereby, a local distribution of dissolved nitrogen concentration isproduced in the mixed molten liquid 2103. Moreover, not only providing aspecial shape of the inner wall of the mixed molten liquid holdingvessel 2102 but also some special member, such as a jig, a mechanicaldevice or the like, may be provided/attached, other than the vessel 2102itself, in the vessel 2102, for the same purpose.

[0249] Moreover, in each of the above-mentioned embodiments, Na is usedas a metal (alkaline metal) having a low melting point and a high vaporpressure. However, instead of Na, potassium (K) or the like may be used.That is, as the alkaline metal, any alkaline metal may be used as longas it becomes a molten liquid at a temperature at which a crystal of agroup-III nitride may grow.

[0250] Moreover, although a case where Ga is used as a substance whichat least contains a group-III metallic element has been described ineach of the above-mentioned embodiments, a metal of a simple substance,such as Al, In, or any mixture thereof, an alloy, etc. may also be usedinstead of Ga.

[0251] Moreover, although a nitrogen gas is used in each of theabove-mentioned embodiments as a substance which at least contains anitrogen element, another gas such as NH₃ may be used instead of thenitrogen gas.

[0252] By carrying out crystal growth of a group-III nitride crystalusing the crystal growth method according to the present inventiondescribed above and the crystal growth apparatus according to thepresent invention, a large-sized group-III nitride crystal can beprovided at low cost.

[0253] As an example of the growth method of a group-III nitride crystalaccording to the present invention described above, Ga is used as thegroup-III metal, a nitrogen gas is used as the nitrogen material, Na isused as the flux, a temperature of the reaction vessel and flux vesselis made into 750 degrees C., and the nitrogen pressure is fixed at 50kg/cm². A GaN crystal can grow under such conditions.

[0254] Moreover, a group-III nitride semiconductor device can beproduced using the group-III nitride crystal grown up by the growthmethod according to the present invention.

[0255]FIG. 9 shows one example of a configuration of the semiconductordevice according to the present invention, which is the same as thatdescribed above with reference to FIG. 9.

[0256] Since the group-III nitride crystal (GaN crystal) according tothe present invention is used for this semiconductor laser as thesubstrate 301 shown in FIG. 9, there are few crystal defects in thissemiconductor laser device, and, thus, it has a large output and a longlife. Moreover, since the GaN substrate 301 is of n type, the electrode310 can be directly formed on the substrate 301, and, thus, there is noneed to draw out two electrodes of the p side and the n side only fromthe obverse surface as in the first prior art (FIG. 1), and, thus, itbecomes possible to attain cost reduction.

[0257] Furthermore, in the semiconductor device of FIG. 9, it becomespossible to form the light emitting end surface by cleavage, and, also,it becomes possible to perform chip separation by cleavage. Thus, itbecomes possible to realize a high-quality device at low cost.

[0258] In addition, although InGaN MQW is used as the activity layer inthe above-mentioned example, it is also possible to shorten thewavelength of light emitted by using AlGaN MQW as the activity layer,instead. According to the present invention, light emission from a deeplevel is reduced as the GaN substrate thus has few defects and fewimpurities. Accordingly, it is possible to thus provide a light-emissiondevice having a high efficiency even when the wavelength of the lightemitted is shortened.

[0259] Specifically, a light-emission device which emits light having awavelength shorter than 400 nm (light-emission device which has asatisfactory performance even in the ultraviolet region) as thegroup-III nitride semiconductor device can be provided. That is,according to the prior art, the light-emission spectrum of a GaN film issuch that most of the lightemission is made from a deep level.Accordingly, the device characteristic is not satisfactory for thewavelength shorter than 400 nm. In contrast thereto, according to thepresent invention, the light-emission device having the satisfactorycharacteristic also for the ultraviolet region can be provided.

[0260] Further, any combination of the above-described embodiments maybe included in the scope of the present invention.

[0261] Moreover, although each of the above-mentioned embodiments is anapplication of the present invention to an optical device, the presentinvention may also be applied to an electronic device. That is, by usinga GaN substrate with few defects according to the present invention, aGaN-family thin film formed thereon by epitaxial growth also has fewcrystal defects. Consequently, the leak current can be well controlled,a career confining effect when a quantum structure is made can beimproved, for example. Thus, a high-performance device can be achievedaccording to the present invention.

[0262] Further, the present invention is not limited to theabove-described embodiments, and variations and modifications may bemade without departing from the scope of the present invention.

[0263] The present application is based on Japanese priorityapplications Nos. 2000-318723, 2000-318988 and 2000-324272, filed onOct. 19, 2000, Oct. 19, 2000 and Oct. 24, 2000, the entire contents ofwhich are hereby incorporated by reference.

What is claimed is:
 1. A crystal growth method, comprising the steps of:a) supplying a nitrogen material into a reaction vessel in which a mixedmolten liquid comprising an alkaline metal and a group-III metal; and b)growing a crystal of a group-III nitride using the mixed molten liquidand the nitrogen material supplied in said step a) in said reactionvessel, wherein a provision is made such as to cause a vapor of thealkaline metal to stay inside said reaction vessel.
 2. A crystal growthmethod, comprising the steps of: a) supplying a nitrogen material into areaction vessel in which a mixed molten liquid comprising an alkalinemetal and a group-III metal; and b) growing a crystal of a group-IIInitride using the mixed molten liquid and the nitrogen material broughtin by said step a) in said reaction vessel, wherein a provision is madesuch as to prevent a vapor of the alkaline metal from blocking a zonethrough which the nitrogen material is supplied from the outside of saidreaction vessel.
 3. The method as claimed in claim 2, wherein atemperature in said reaction vessel above the surface of the mixedmolten liquid is controlled so as to prevent the vapor of the alkalinemetal from condensing.
 4. The method as claimed in claim 2, wherein thetemperature of said zone is controlled.
 5. The method as claimed inclaim 1, wherein: another reaction vessel is provided outside of saidreaction vessel; the nitrogen material is brought into the innerreaction vessel through the thus-provided outer reaction vessel; and aprovision is made such as to allow the nitrogen material to be broughtinto said inner reaction vessel from said outer reaction vessel, and,also, to cause the vapor of the alkaline metal to stay inside said innerreaction vessel.
 6. The method as claimed in claim 2, wherein thenitrogen material is supplied horizontally or from a direction below thehorizontal direction.
 7. A crystal growth apparatus, comprising: areaction vessel holding a mixed molten liquid comprising an alkalinemetal and a group-III metal; a first heating device heating the mixedmolten liquid so as to enable crystal growth therein; and a secondheating device heating above the surface of the mixed molten liquid soas to prevent the vapor of the alkaline metal above the surface of themixed molten liquid from condensing.
 8. A crystal growth apparatuscomprising: a reaction vessel holding a mixed molten liquid comprisingan alkaline metal and a group-III metal; and a heating device heating azone-through which a nitrogen material is supplied externally into saidreaction vessel.
 9. The apparatus as claimed in claim 7, wherein:another reaction vessel is provided outside of said reaction vessel; thenitrogen material is brought into the inner reaction vessel through thethus-provided outer reaction vessel; and a provision is made such as toallow the nitrogen material to be brought into said inner reactionvessel from said outer reaction vessel, and, also, to cause the vapor ofthe alkaline metal to stay inside said inner reaction vessel.
 10. Theapparatus as claimed in claim 8, wherein the nitrogen material issupplied horizontally or from a direction below the horizontaldirection.
 11. A crystal growth method comprising the steps of: a)carrying out crystal growth in a reaction vessel of a group-III nitridecomprising a group-III metal and a nitrogen from an alkaline metal, asubstance comprising the group-III metal, and a substance comprising thenitrogen; and b) maintaining a growth condition for a crystal of thegroup-III nitride at a condition at which the crystal growth starts;then, c) maintaining the growth condition at a condition at which thecrystal growth stops; and, then, d) again setting the condition at whichthe crystal growth starts.
 12. The method as claimed in claim 11,wherein: said step b) maintains the temperature of a zone in which acrystal of the group-III nitride grows at a temperature at which thecrystal growth starts; said step c) lowers the temperature of said zoneto a temperature such that no alloy is formed between the group-IIImetal and another metal, and maintaining the temperature; and said stepd) increases the temperature to the temperature at which the crystalgrowth starts again.
 13. The method as claimed in claim 12, whereinincrease and decrease of the temperature are performed several times.14. The method as claimed in claim 12, wherein the substance comprisingthe nitrogen in a form of a gas, and the gas is supplied into thereaction vessel continuously at a predetermined pressure.
 15. The methodas claimed in claim 12, wherein the substance comprising the group-IIImetal is additionally provided at the time the temperature is lowered.16. The method as claimed in claim 11, wherein: said step b) maintainsan effective pressure of the substance comprising the nitride in a forma gas in a zone in which a crystal of the group-III nitride grows at apressure at which the crystal growth starts; said step c) lowers theeffective pressure of the nitrogen gas in said zone to a pressure suchthat the crystal growth stops, and maintaining the pressure; and saidstep d) increases the effective pressure of the nitrogen gas to thepressure at which the crystal growth starts again.
 17. The method asclaimed in claim 16, wherein increase and decrease of the effectivepressure of the nitrogen gas are performed several times.
 18. The methodas claimed in claim 16, wherein the substance comprising the group-IIImetal is additionally provided at the time the effective pressure of thenitrogen gas is lowered.
 19. A crystal growth apparatus comprising: areaction vessel in which crystal growth is performed of a group-IIInitride comprising a group-III metal and a nitrogen from an alkalinemetal, a substance comprising the group-III metal, and a substancecomprising the nitrogen; and a unit maintaining a growth condition for acrystal of the group-III nitride at a condition at which the crystalgrowth starts; then, maintaining the growth condition at a condition atwhich the crystal growth stops; and, then, again setting the conditionat which the crystal growth starts.
 20. The apparatus as claimed inclaim 19, wherein said unit comprises a heating device heating a zone inwhich a crystal of the group-III nitride grows.
 21. The apparatus asclaimed in claim 19, wherein said unit comprises a pressure controldevice controlling an effective pressure of the substance comprising thenitrogen in a form of a gas in a zone in which a crystal of thegroup-III nitride grows.
 22. A crystal growth method, comprising thesteps of: a) forming a mixed molten liquid comprising an alkaline metaland a substance comprising a group-III metal in a liquid holding vessel;b) growing in said liquid holding vessel a crystal of a group-IIInitride comprising the group-III metal and nitride from the mixed moltenliquid and a substance comprising the nitride; c) creating a localconcentration distribution of dissolved nitrogen in the mixed moltenliquid in said liquid holding vessel during said step b).
 23. The methodas claimed in claim 22, wherein said liquid holding vessel has an innershape such as to create the local concentration distribution of thedissolved nitrogen in the mixed molten liquid.
 24. The method as claimedin claim 23, wherein said inner shape of said liquid holding vessel issuch that the cross sectional area becomes smaller downward.
 25. Themethod as claimed in claim 23, wherein said inner shape of said liquidholding vessel is such that the cross sectional area is reducedpartially.
 26. The method as claimed in claim 23, wherein said innershape of said liquid holding vessel is such that the cross sectionalarea becomes smaller downward first, and, then, the cross sectional areais uniform downward from a mid height.
 27. The method as claimed inclaim 23, wherein said inner shape of said liquid holding vessel is suchthat the cross sectional area becomes smaller downward first, and, then,the cross sectional area becomes larger downward from a mid height. 28.A crystal growth apparatus, comprising: a liquid holding vessel in whicha mixed molten liquid comprising an alkaline metal and a substancecomprising a group-III metal is formed; and a unit growing in saidliquid holding vessel a crystal of a group-III nitride comprising thegroup-III metal and nitride from the mixed molten liquid and a substancecomprising the nitride, wherein said liquid holding vessel has an innershape such as to create a local concentration distribution of dissolvednitrogen in the mixed molten liquid.
 29. The apparatus as claimed inclaim 28, wherein said inner shape of said liquid holding vessel is suchthat the cross sectional area becomes smaller downward.
 30. Theapparatus as claimed in claim 28, wherein said inner shape of saidliquid holding vessel is such that the cross sectional area is reducedpartially.
 31. The apparatus as claimed in claim 28, wherein said innershape of said liquid holding vessel is such that the cross sectionalarea becomes smaller downward first, and, then, the cross sectional areais uniform downward from the mid level.
 32. The apparatus as claimed inclaim 28, wherein said inner shape of said liquid holding vessel is suchthat the cross sectional area becomes smaller downward first, and, then,the cross sectional area becomes larger downward from the mid level. 33.The apparatus as claimed in claim 28, wherein said unit comprises aheating device heating the temperature inside said liquid holding vesselso as to enable the crystal growth therein.
 34. The apparatus as claimedin claim 31, wherein said unit comprises a plurality of heating devicesfor creating a predetermined temperature difference between an upperpart and a lower part of said liquid holding vessel.
 35. A group-IIInitride crystal formed in accordance with the crystal growth methodclaimed in claim
 1. 36. A group-III nitride crystal formed in accordancewith the crystal growth method claimed in claim
 2. 37. A group-IIInitride crystal formed by the crystal growth apparatus claimed in claim7.
 38. A group-III nitride crystal formed by the crystal growthapparatus claimed in claim
 8. 39. A group-III nitride crystal formed inaccordance with the crystal growth method claimed in claim
 11. 40. Agroup-III nitride crystal formed by the crystal growth apparatus claimedin claim
 19. 41. A group-III nitride crystal formed in accordance withthe crystal growth method claimed in claim
 22. 42. A group-III nitridecrystal formed by the crystal growth apparatus claimed in claim
 28. 43.A semiconductor device produced employing the group-III nitride crystalclaimed in claim
 35. 44. A semiconductor device produced employing thegroup-III nitride crystal claimed in claim
 36. 45. A semiconductordevice produced employing the group-III nitride crystal claimed in claim37.
 46. A semiconductor device produced employing the group-III nitridecrystal claimed in claim
 38. 47. A semiconductor device producedemploying the group-III nitride crystal claimed in claim
 39. 48. Asemiconductor device produced employing the group-III nitride crystalclaimed in claim
 40. 49. A semiconductor device produced employing thegroup-III nitride crystal claimed in claim
 41. 50. A semiconductordevice produced employing the group-III nitride crystal claimed in claim42.
 51. The semiconductor device as claimed in claim 43, wherein saiddevice comprises a light-emission diode emitting light of a wavelengthshorter than 400 nm.
 52. The semiconductor device as claimed in claim44, wherein said device comprises a light-emission diode emitting lightof a wavelength shorter than 400 nm.
 53. The semiconductor device asclaimed in claim 45, wherein said device comprises a light-emissiondiode emitting light of a wavelength shorter than 400 nm.
 54. Thesemiconductor device as claimed in claim 46, wherein said devicecomprises a light-emission diode emitting light of a wavelength shorterthan 400 nm.
 55. The semiconductor device as claimed in claim 47,wherein said device comprises a light-emission diode emitting light of awavelength shorter than 400 nm.
 56. The semiconductor device as claimedin claim 48, wherein said device comprises a light-emission diodeemitting light of a wavelength shorter than 400 nm.
 57. Thesemiconductor device as claimed in claim 49, wherein said devicecomprises a light-emission diode emitting light of a wavelength shorterthan 400 nm.
 58. The semiconductor device as claimed in claim 50,wherein said device comprises a light-emission diode emitting light of awavelength shorter than 400 nm.